Schedule of Notional Amounts of Derivative Positions (Details) - USD ($) $ in Thousands |
3 Months Ended |
9 Months Ended |
Sep. 30, 2015 |
Sep. 30, 2014 |
Sep. 30, 2015 |
Sep. 30, 2014 |
Derivative [Line Items] |
|
|
|
|
Derivative, Notional Amount, Beginning Balance |
$ 27,401,335
|
$ 43,379,217
|
$ 48,115,523
|
$ 37,366,610
|
Derivative, Notional Amount, Additions |
6,930,287
|
38,371,670
|
30,475,551
|
68,977,405
|
Derivative, Notional Amount, Settlement Termination Expiration or Exercise |
6,014,042
|
24,734,906
|
50,273,494
|
49,328,034
|
Derivative, Notional Amount, Ending Balance |
28,317,580
|
57,015,981
|
28,317,580
|
57,015,981
|
Derivative, Average Notional Amount |
27,222,458
|
55,307,546
|
32,531,397
|
46,500,488
|
Gain (Loss) on Sale of Derivatives |
(78,283)
|
(49,047)
|
(160,665)
|
(86,237)
|
Inverse Interest-Only Securities [Member] |
|
|
|
|
Derivative [Line Items] |
|
|
|
|
Derivative, Notional Amount, Beginning Balance |
1,049,743
|
1,323,650
|
1,168,226
|
1,525,845
|
Derivative, Notional Amount, Additions |
0
|
0
|
12,563
|
0
|
Derivative, Notional Amount, Settlement Termination Expiration or Exercise |
63,842
|
111,685
|
194,888
|
313,880
|
Derivative, Notional Amount, Ending Balance |
985,901
|
1,211,965
|
985,901
|
1,211,965
|
Derivative, Average Notional Amount |
1,020,199
|
1,261,098
|
1,081,376
|
1,367,332
|
Gain (Loss) on Sale of Derivatives |
0
|
221
|
64
|
414
|
Interest Rate Swap [Member] |
|
|
|
|
Derivative [Line Items] |
|
|
|
|
Derivative, Notional Amount, Beginning Balance |
16,225,523
|
23,628,148
|
18,584,000
|
19,619,000
|
Derivative, Notional Amount, Additions |
5,280,000
|
12,206,450
|
22,393,227
|
23,615,598
|
Derivative, Notional Amount, Settlement Termination Expiration or Exercise |
7,480,000
|
8,063,943
|
26,951,704
|
15,463,943
|
Derivative, Notional Amount, Ending Balance |
14,025,523
|
27,770,655
|
14,025,523
|
27,770,655
|
Derivative, Average Notional Amount |
15,371,175
|
28,607,951
|
16,753,347
|
23,778,725
|
Gain (Loss) on Sale of Derivatives |
(24,948)
|
4,197
|
(92,816)
|
1,193
|
Credit Default Swap [Member] |
|
|
|
|
Derivative [Line Items] |
|
|
|
|
Derivative, Notional Amount, Beginning Balance |
125,000
|
125,000
|
125,000
|
427,073
|
Derivative, Notional Amount, Additions |
0
|
0
|
0
|
0
|
Derivative, Notional Amount, Settlement Termination Expiration or Exercise |
0
|
0
|
0
|
302,073
|
Derivative, Notional Amount, Ending Balance |
125,000
|
125,000
|
125,000
|
125,000
|
Derivative, Average Notional Amount |
125,000
|
125,000
|
125,000
|
142,940
|
Gain (Loss) on Sale of Derivatives |
0
|
0
|
0
|
(13,705)
|
Interest Rate Swaption [Member] |
|
|
|
|
Derivative [Line Items] |
|
|
|
|
Derivative, Notional Amount, Beginning Balance |
9,410,000
|
11,450,000
|
12,410,000
|
5,130,000
|
Derivative, Notional Amount, Additions |
0
|
2,710,000
|
7,050,000
|
9,860,000
|
Derivative, Notional Amount, Settlement Termination Expiration or Exercise |
(600,000)
|
(6,500,000)
|
9,450,000
|
(7,330,000)
|
Derivative, Notional Amount, Ending Balance |
10,010,000
|
7,660,000
|
10,010,000
|
7,660,000
|
Derivative, Average Notional Amount |
9,481,739
|
7,972,500
|
10,862,930
|
9,117,546
|
Gain (Loss) on Sale of Derivatives |
(36,960)
|
(49,509)
|
(32,168)
|
(52,905)
|
Forward Contracts [Member] |
|
|
|
|
Derivative [Line Items] |
|
|
|
|
Derivative, Notional Amount, Beginning Balance |
1,024,000
|
372,000
|
1,325,000
|
603,000
|
Derivative, Notional Amount, Additions |
468,000
|
3,316,000
|
11,330,000
|
6,240,000
|
Derivative, Notional Amount, Settlement Termination Expiration or Exercise |
2,274,000
|
(2,998,000)
|
13,437,000
|
(4,947,000)
|
Derivative, Notional Amount, Ending Balance |
782,000
|
690,000
|
782,000
|
690,000
|
Derivative, Average Notional Amount |
(343,272)
|
(830,435)
|
(729,916)
|
(673,509)
|
Gain (Loss) on Sale of Derivatives |
(13,615)
|
(5,177)
|
(38,461)
|
(19,854)
|
Short US Treasury Securities [Member] |
|
|
|
|
Derivative [Line Items] |
|
|
|
|
Derivative, Notional Amount, Beginning Balance |
0
|
0
|
0
|
0
|
Derivative, Notional Amount, Additions |
0
|
0
|
(50,000)
|
(125,000)
|
Derivative, Notional Amount, Settlement Termination Expiration or Exercise |
0
|
0
|
50,000
|
125,000
|
Derivative, Notional Amount, Ending Balance |
0
|
0
|
0
|
0
|
Derivative, Average Notional Amount |
0
|
0
|
0
|
458
|
Gain (Loss) on Sale of Derivatives |
0
|
0
|
125
|
2
|
Options Held [Member] |
|
|
|
|
Derivative [Line Items] |
|
|
|
|
Derivative, Notional Amount, Beginning Balance |
0
|
0
|
2,000,000
|
0
|
Derivative, Notional Amount, Additions |
1,000,000
|
2,000,000
|
1,250,000
|
3,500,000
|
Derivative, Notional Amount, Settlement Termination Expiration or Exercise |
0
|
0
|
2,250,000
|
(1,500,000)
|
Derivative, Notional Amount, Ending Balance |
1,000,000
|
2,000,000
|
1,000,000
|
2,000,000
|
Derivative, Average Notional Amount |
163,043
|
336,957
|
(183,150)
|
498,168
|
Gain (Loss) on Sale of Derivatives |
0
|
(1,016)
|
7,796
|
(6,348)
|
Treasury Lock [Member] |
|
|
|
|
Derivative [Line Items] |
|
|
|
|
Derivative, Notional Amount, Beginning Balance |
0
|
|
0
|
|
Derivative, Notional Amount, Additions |
0
|
|
500,000
|
|
Derivative, Notional Amount, Settlement Termination Expiration or Exercise |
0
|
|
500,000
|
|
Derivative, Notional Amount, Ending Balance |
0
|
|
0
|
|
Derivative, Average Notional Amount |
0
|
|
916
|
|
Gain (Loss) on Sale of Derivatives |
0
|
|
(837)
|
|
Swap [Member] |
|
|
|
|
Derivative [Line Items] |
|
|
|
|
Derivative, Notional Amount, Beginning Balance |
0
|
6,000,000
|
14,000,000
|
10,000,000
|
Derivative, Notional Amount, Additions |
0
|
24,000,000
|
6,000,000
|
36,000,000
|
Derivative, Notional Amount, Settlement Termination Expiration or Exercise |
0
|
12,000,000
|
20,000,000
|
28,000,000
|
Derivative, Notional Amount, Ending Balance |
0
|
18,000,000
|
0
|
18,000,000
|
Derivative, Average Notional Amount |
0
|
15,032,609
|
3,018,315
|
10,219,780
|
Gain (Loss) on Sale of Derivatives |
0
|
344
|
7,694
|
2,771
|
Total Return Swap [Member] |
|
|
|
|
Derivative [Line Items] |
|
|
|
|
Derivative, Notional Amount, Beginning Balance |
988,409
|
576,478
|
598,459
|
49,629
|
Derivative, Notional Amount, Additions |
176,807
|
49,669
|
1,601,350
|
586,550
|
Derivative, Notional Amount, Settlement Termination Expiration or Exercise |
277,252
|
14,162
|
1,311,845
|
24,194
|
Derivative, Notional Amount, Ending Balance |
887,964
|
611,985
|
887,964
|
611,985
|
Derivative, Average Notional Amount |
828,323
|
593,092
|
968,223
|
381,913
|
Gain (Loss) on Sale of Derivatives |
(2,368)
|
0
|
(11,296)
|
0
|
Forward Purchase Commitments [Member] |
|
|
|
|
Derivative [Line Items] |
|
|
|
|
Derivative, Notional Amount, Beginning Balance |
626,660
|
647,941
|
554,838
|
12,063
|
Derivative, Notional Amount, Additions |
941,480
|
721,551
|
3,048,411
|
1,780,257
|
Derivative, Notional Amount, Settlement Termination Expiration or Exercise |
1,066,948
|
1,043,116
|
3,102,057
|
1,465,944
|
Derivative, Notional Amount, Ending Balance |
501,192
|
326,376
|
501,192
|
326,376
|
Derivative, Average Notional Amount |
576,251
|
547,904
|
634,356
|
320,117
|
Gain (Loss) on Sale of Derivatives |
$ (392)
|
$ 1,893
|
$ (766)
|
$ 2,195
|