Derivative Instruments and Hedging Activities Schedule of Total Return Swaps (Details) - USD ($)
$ in Thousands |
Sep. 30, 2016 |
Jun. 30, 2016 |
Dec. 31, 2015 |
Sep. 30, 2015 |
Jun. 30, 2015 |
Dec. 31, 2014 |
| Derivative [Line Items] |
|
|
|
|
|
|
| Derivative, Notional Amount |
$ (22,062,904)
|
$ (26,141,370)
|
$ (21,998,381)
|
$ (28,317,580)
|
$ (27,401,335)
|
$ (48,115,523)
|
| Total Return Swap [Member] |
|
|
|
|
|
|
| Derivative [Line Items] |
|
|
|
|
|
|
| Derivative, Notional Amount |
(96,248)
|
$ (588,037)
|
(889,418)
|
$ (887,964)
|
$ (988,409)
|
$ (598,459)
|
| Derivative, Fair Value, Net |
(752)
|
|
1,645
|
|
|
|
| Derivative, Cost |
686
|
|
1,383
|
|
|
|
| Derivative, Unrealized Gains (Losses) |
(1,438)
|
|
262
|
|
|
|
| Maturity Date, 1/12/2043 [Member] | Total Return Swap [Member] |
|
|
|
|
|
|
| Derivative [Line Items] |
|
|
|
|
|
|
| Derivative, Notional Amount |
(47,910)
|
|
(369,639)
|
|
|
|
| Derivative, Fair Value, Net |
(363)
|
|
456
|
|
|
|
| Derivative, Cost |
320
|
|
866
|
|
|
|
| Derivative, Unrealized Gains (Losses) |
(683)
|
|
(410)
|
|
|
|
| Maturity Date, 1/12/2044 [Member] | Total Return Swap [Member] |
|
|
|
|
|
|
| Derivative [Line Items] |
|
|
|
|
|
|
| Derivative, Notional Amount |
(48,338)
|
|
(325,003)
|
|
|
|
| Derivative, Fair Value, Net |
(389)
|
|
350
|
|
|
|
| Derivative, Cost |
366
|
|
1,679
|
|
|
|
| Derivative, Unrealized Gains (Losses) |
(755)
|
|
(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 |
(16,759,324)
|
|
(21,735,997)
|
|
|
|
| Derivative, Fair Value, Net |
199,013
|
|
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
|
|
|
|