Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Schedule of Interest Rate Swaptions (Details)

v3.19.1
Derivative Instruments and Hedging Activities Schedule of Interest Rate Swaptions (Details) - USD ($)
 3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Mar. 31, 2018
Dec. 31, 2017
Derivative [Line Items]        
Notional $ (58,777,783,000) $ (36,528,169,000) $ (18,429,288,000) $ (31,226,878,000)
Interest Rate Swaption [Member] | Long [Member] | Variable Income Interest Rate [Member]        
Derivative [Line Items]        
Cost Basis (2,134,000) (13,255,000)    
Fair Value $ (589,000) $ (8,422,000)    
Weighted Average Remaining Maturity 5 months 9 days 7 months 28 days    
Interest Rate Swaption [Member] | Long [Member] | Variable Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member]        
Derivative [Line Items]        
Cost Basis $ (2,134,000) $ (4,855,000)    
Fair Value $ (589,000) $ (2,430,000)    
Weighted Average Remaining Maturity 5 months 9 days 5 months 4 days    
Interest Rate Swaption [Member] | Long [Member] | Variable Income Interest Rate [Member] | Six Months or Longer Remaining Maturity [Member]        
Derivative [Line Items]        
Cost Basis   $ (8,400,000)    
Fair Value   $ (5,992,000)    
Weighted Average Remaining Maturity   8 months 18 days    
Interest Rate Swaption [Member] | Long [Member] | Fixed Income Interest Rate [Member]        
Derivative [Line Items]        
Cost Basis $ (19,960,000)      
Fair Value $ (33,742,000)      
Weighted Average Remaining Maturity 7 months 26 days      
Interest Rate Swaption [Member] | Long [Member] | Fixed Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member]        
Derivative [Line Items]        
Cost Basis $ (8,560,000)      
Fair Value $ (19,092,000)      
Weighted Average Remaining Maturity 5 months 14 days      
Interest Rate Swaption [Member] | Long [Member] | Fixed Income Interest Rate [Member] | Six Months or Longer Remaining Maturity [Member]        
Derivative [Line Items]        
Cost Basis $ (11,400,000)      
Fair Value $ (14,650,000)      
Weighted Average Remaining Maturity 11 months 23 days      
Interest Rate Swaption [Member] | Short [Member] | Fixed Income Interest Rate [Member]        
Derivative [Line Items]        
Cost Basis $ (4,750,000) $ (13,255,000)    
Fair Value $ 10,659,000 $ (21,878,000)    
Weighted Average Remaining Maturity 5 months 9 days 7 months 16 days    
Interest Rate Swaption [Member] | Short [Member] | Fixed Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member]        
Derivative [Line Items]        
Cost Basis $ (4,750,000) $ (4,855,000)    
Fair Value $ 10,659,000 $ (9,001,000)    
Weighted Average Remaining Maturity 5 months 9 days 4 months 24 days    
Interest Rate Swaption [Member] | Short [Member] | Fixed Income Interest Rate [Member] | Six Months or Longer Remaining Maturity [Member]        
Derivative [Line Items]        
Cost Basis   $ (8,400,000)    
Fair Value   $ (12,877,000)    
Weighted Average Remaining Maturity   8 months 18 days    
Underlying Swap [Member] | Long [Member] | Variable Income Interest Rate [Member]        
Derivative [Line Items]        
Weighted Average Remaining Maturity 10 years 10 years    
Notional $ (700,000,000) $ (1,700,000,000)    
Underlying Swap [Member] | Long [Member] | Variable Income Interest Rate [Member] | London Interbank Offered Rate (LIBOR) [Member]        
Derivative [Line Items]        
Weighted Average Fixed Interest Rate 3.09% 3.15%    
Underlying Swap [Member] | Long [Member] | Variable Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member]        
Derivative [Line Items]        
Weighted Average Remaining Maturity 10 years 10 years    
Notional $ (700,000,000) $ (900,000,000)    
Underlying Swap [Member] | Long [Member] | Variable Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member] | London Interbank Offered Rate (LIBOR) [Member]        
Derivative [Line Items]        
Weighted Average Fixed Interest Rate 3.09% 3.16%    
Underlying Swap [Member] | Long [Member] | Variable Income Interest Rate [Member] | Six Months or Longer Remaining Maturity [Member]        
Derivative [Line Items]        
Weighted Average Remaining Maturity   10 years    
Notional   $ (800,000,000)    
Underlying Swap [Member] | Long [Member] | Variable Income Interest Rate [Member] | Six Months or Longer Remaining Maturity [Member] | London Interbank Offered Rate (LIBOR) [Member]        
Derivative [Line Items]        
Weighted Average Fixed Interest Rate   3.14%    
Underlying Swap [Member] | Long [Member] | Fixed Income Interest Rate [Member]        
Derivative [Line Items]        
Weighted Average Remaining Maturity 10 years      
Notional $ (6,000,000,000)      
Underlying Swap [Member] | Long [Member] | Fixed Income Interest Rate [Member] | London Interbank Offered Rate (LIBOR) [Member]        
Derivative [Line Items]        
Weighted Average Fixed Interest Rate 2.04%      
Underlying Swap [Member] | Long [Member] | Fixed Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member]        
Derivative [Line Items]        
Weighted Average Remaining Maturity 10 years      
Notional $ (4,500,000,000)      
Underlying Swap [Member] | Long [Member] | Fixed Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member] | London Interbank Offered Rate (LIBOR) [Member]        
Derivative [Line Items]        
Weighted Average Fixed Interest Rate 2.03%      
Underlying Swap [Member] | Long [Member] | Fixed Income Interest Rate [Member] | Six Months or Longer Remaining Maturity [Member]        
Derivative [Line Items]        
Weighted Average Remaining Maturity 10 years      
Notional $ (1,500,000,000)      
Underlying Swap [Member] | Long [Member] | Fixed Income Interest Rate [Member] | Six Months or Longer Remaining Maturity [Member] | London Interbank Offered Rate (LIBOR) [Member]        
Derivative [Line Items]        
Weighted Average Fixed Interest Rate 2.09%      
Underlying Swap [Member] | Short [Member] | Fixed Income Interest Rate [Member]        
Derivative [Line Items]        
Weighted Average Remaining Maturity 10 years 10 years    
Notional $ (800,000,000) $ (1,637,000,000)    
Underlying Swap [Member] | Short [Member] | Fixed Income Interest Rate [Member] | London Interbank Offered Rate (LIBOR) [Member]        
Derivative [Line Items]        
Weighted Average Fixed Interest Rate 2.41% 2.65%    
Underlying Swap [Member] | Short [Member] | Fixed Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member]        
Derivative [Line Items]        
Weighted Average Remaining Maturity 10 years 10 years    
Notional $ (800,000,000) $ (845,000,000)    
Underlying Swap [Member] | Short [Member] | Fixed Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member] | London Interbank Offered Rate (LIBOR) [Member]        
Derivative [Line Items]        
Weighted Average Fixed Interest Rate 2.41% 2.66%    
Underlying Swap [Member] | Short [Member] | Fixed Income Interest Rate [Member] | Six Months or Longer Remaining Maturity [Member]        
Derivative [Line Items]        
Weighted Average Remaining Maturity   10 years    
Notional   $ (792,000,000)    
Underlying Swap [Member] | Short [Member] | Fixed Income Interest Rate [Member] | Six Months or Longer Remaining Maturity [Member] | London Interbank Offered Rate (LIBOR) [Member]        
Derivative [Line Items]        
Weighted Average Fixed Interest Rate   2.64%