Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Derivative Instruments and Hedging Activities Schedule of Interest Rate Swaptions (Details) - USD ($)
 6 Months Ended 12 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Mar. 31, 2018
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Derivative [Line Items]            
Notional $ (28,618,861,000) $ (31,226,878,000) $ (18,429,288,000) $ (16,988,116,000) $ (15,935,535,000) $ (18,802,500,000)
Interest Rate Swaption [Member] | Long [Member] | Variable Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member]            
Derivative [Line Items]            
Cost Basis (9,680,000) (21,380,000)        
Fair Value $ 10,664,000 $ 17,736,000        
Weighted Average Remaining Maturity 26 days 4 months 1 day        
Interest Rate Swaption [Member] | Long [Member] | Fixed Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member]            
Derivative [Line Items]            
Cost Basis   $ (4,660,000)        
Fair Value   $ 2,982,000        
Weighted Average Remaining Maturity   3 months 22 days        
Interest Rate Swaption [Member] | Short [Member] | Variable Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member]            
Derivative [Line Items]            
Cost Basis   $ (7,950,000)        
Fair Value   $ 5,619,000        
Weighted Average Remaining Maturity   4 months 20 days        
Interest Rate Swaption [Member] | Short [Member] | Variable Income Interest Rate [Member] | Six Months or Longer Remaining Maturity [Member]            
Derivative [Line Items]            
Cost Basis $ (6,808,000)          
Fair Value $ (4,846,000)          
Weighted Average Remaining Maturity 8 months 6 days          
Interest Rate Swaption [Member] | Short [Member] | Fixed Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member]            
Derivative [Line Items]            
Cost Basis $ (9,730,000) $ (16,260,000)        
Fair Value $ (3,187,000) $ 4,694,000        
Weighted Average Remaining Maturity 3 months 23 days 5 months 5 days        
Interest Rate Swaption [Member] | Short [Member] | Fixed Income Interest Rate [Member] | Six Months or Longer Remaining Maturity [Member]            
Derivative [Line Items]            
Cost Basis $ (6,962,000)          
Fair Value $ (5,462,000)          
Weighted Average Remaining Maturity 8 months 6 days          
Underlying Swap [Member] | Long [Member] | Variable Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member]            
Derivative [Line Items]            
Weighted Average Remaining Maturity 5 years 10 months 19 days 3 years 9 months        
Notional $ (2,545,000,000) $ (7,200,000,000)        
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 2.91% 2.27%        
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   $ (2,300,000,000)        
Weighted Average Fixed Interest Rate   2.095%        
Underlying Swap [Member] | Short [Member] | Variable Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member]            
Derivative [Line Items]            
Weighted Average Remaining Maturity   10 years        
Notional   $ (1,693,000,000)        
Underlying Swap [Member] | Short [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   2.70%        
Underlying Swap [Member] | Short [Member] | Variable Income Interest Rate [Member] | Six Months or Longer Remaining Maturity [Member]            
Derivative [Line Items]            
Weighted Average Remaining Maturity 10 years          
Notional $ (280,000,000)          
Underlying Swap [Member] | Short [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 2.99%          
Underlying Swap [Member] | Short [Member] | Fixed Income Interest Rate [Member] | Less Than Six Months Remaining Maturity [Member]            
Derivative [Line Items]            
Weighted Average Remaining Maturity 5 years 10 months 13 days 5 years 7 months 9 days        
Notional $ (2,723,000,000) $ (5,141,000,000)        
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 2.40% 1.89%        
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 $ (280,000,000)          
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 2.99%