Annual report pursuant to Section 13 and 15(d)

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

v3.6.0.2
Derivative Instruments and Hedging Activities Schedule of Total Return Swaps (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Derivative [Line Items]      
Derivative, Notional Amount $ (18,802,500) $ (21,998,381) $ (48,115,523)
Total Return Swap [Member]      
Derivative [Line Items]      
Derivative, Notional Amount (90,593) (889,418) $ (598,459)
Derivative, Fair Value, Net (17) 1,645  
Derivative, Cost 686 1,383  
Derivative, Unrealized Gains (Losses) (703) 262  
Maturity Date, 1/12/2043 [Member] | Total Return Swap [Member]      
Derivative [Line Items]      
Derivative, Notional Amount (45,083) (369,639)  
Derivative, Fair Value, Net (5) 456  
Derivative, Cost 320 866  
Derivative, Unrealized Gains (Losses) (325) (410)  
Maturity Date, 1/12/2044 [Member] | Total Return Swap [Member]      
Derivative [Line Items]      
Derivative, Notional Amount (45,510) (325,003)  
Derivative, Fair Value, Net (12) 350  
Derivative, Cost 366 1,679  
Derivative, Unrealized Gains (Losses) (378) (1,329)  
Maturity Date, 1/12/2045 [Member] | Total Return Swap [Member]      
Derivative [Line Items]      
Derivative, Notional Amount   (194,776)  
Derivative, Fair Value, Net   839  
Derivative, Cost   1,162  
Derivative, Unrealized Gains (Losses)   2,001  
Derivative Financial Instruments, Assets [Member]      
Derivative [Line Items]      
Derivative, Notional Amount (21,708,907) (21,735,997)  
Derivative, Fair Value, Net 324,182 271,509  
Derivative Financial Instruments, Assets [Member] | Total Return Swap [Member]      
Derivative [Line Items]      
Derivative, Notional Amount 0 (889,418)  
Derivative, Fair Value, Net $ 0 $ 1,645