Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Schedule of Total Return Swaps (Details)

v3.7.0.1
Derivative Instruments and Hedging Activities Schedule of Total Return Swaps (Details) - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Mar. 31, 2016
Dec. 31, 2015
Derivative [Line Items]        
Derivative, Notional Amount $ (15,935,535) $ (18,802,500) $ (26,390,596) $ (21,998,381)
Total Return Swap [Member]        
Derivative [Line Items]        
Derivative, Notional Amount (87,269) (90,593) $ (868,145) $ (889,418)
Derivative, Fair Value, Net (714) (17)    
Derivative, Cost (686) (686)    
Derivative, Unrealized Gains (Losses) (1,400) (703)    
Maturity Date, 1/12/2043 [Member] | Total Return Swap [Member]        
Derivative [Line Items]        
Derivative, Notional Amount (43,403) (45,083)    
Derivative, Fair Value, Net (386) (5)    
Derivative, Cost (320) (320)    
Derivative, Unrealized Gains (Losses) (706) (325)    
Maturity Date, 1/12/2044 [Member] | Total Return Swap [Member]        
Derivative [Line Items]        
Derivative, Notional Amount (43,866) (45,510)    
Derivative, Fair Value, Net (328) (12)    
Derivative, Cost (366) (366)    
Derivative, Unrealized Gains (Losses) (694) (378)    
Derivative Financial Instruments, Assets [Member]        
Derivative [Line Items]        
Derivative, Notional Amount (21,576,266) (21,708,907)    
Derivative, Fair Value, Net 253,564 324,182    
Derivative Financial Instruments, Assets [Member] | Total Return Swap [Member]        
Derivative [Line Items]        
Derivative, Notional Amount 0 0    
Derivative, Fair Value, Net $ 0 $ 0