Fair Value - Level III (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Total realized and unrealized gains (losses):
Included in earnings: OTTI	$ (109)		$ (109)
Included in earnings: Net accretion			8,007	$ 7,349
Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	58,676,362	$ 82,634,467	64,941,714	74,836,009
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(5,484,119)	(4,190,909)	(11,635,546)	(8,043,168)
Included in earnings: OTTI	(109)		(109)
Included in earnings: Net accretion	3,302	3,742	7,188	7,157
Included in OCI	4,907	5,951	6,753	2,551
Purchases / Originations	564,501	359,455	1,010,388	634,668
Sales	(291,882)	(219,638)	(481,612)	(476,602)
Issuances	(5,429)		(10,188)	(596)
Cash repayments / receipts	(26,559)	(8,588)	(73,546)	(21,989)
Transfers into Level III	(319,457)	(557,543)	(383,427)	(972,587)
Transfers out of Level III	34,288	35,759	163,740	146,724
Consolidations of VIEs		1,693,694	1,127,952	16,227,974
Deconsolidations of VIEs	(498,674)	(2,534,918)	(2,016,176)	(5,118,669)
Balance at the end of the period	52,657,131	77,221,472	52,657,131	77,221,472
Amount of total (losses) gains included in earnings attributable to assets still held at period end	(5,496,891)	(4,197,733)	(11,653,949)	(8,052,865)
VIE liabilities | Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	(2,161,295)	(3,038,534)	(2,585,369)	(2,552,448)
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	213,503	57,477	598,484	293,600
Issuances	(5,429)		(10,188)	(596)
Cash repayments / receipts	(5,240)	14,922	(36,036)	20,772
Transfers into Level III	(319,457)	(557,543)	(383,427)	(972,587)
Transfers out of Level III	34,288	35,759	163,740	146,724
Consolidations of VIEs		(53,252)		(483,905)
Deconsolidations of VIEs	79,037	519	88,203	7,788
Balance at the end of the period	(2,164,593)	(3,540,652)	(2,164,593)	(3,540,652)
Amount of total (losses) gains included in earnings attributable to assets still held at period end	213,503	57,477	598,484	293,600
Loans held-for-sale | Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	340,266	154,225	63,279	203,865
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	15,406	13,235	25,999	20,126
Purchases / Originations	557,068	288,186	1,002,955	488,756
Sales	(291,182)	(218,369)	(470,478)	(475,333)
Cash repayments / receipts	(11,442)	(171)	(11,639)	(308)
Balance at the end of the period	610,116	237,106	610,116	237,106
Amount of total (losses) gains included in earnings attributable to assets still held at period end	(3,291)	1,810	(3,291)	1,810
RMBS | Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	249,419	210,898	253,915	176,224
Total realized and unrealized gains (losses):
Included in earnings: OTTI	(109)		(109)
Included in earnings: Net accretion	3,302	3,742	7,188	7,157
Included in OCI	4,907	5,951	6,753	2,551
Purchases / Originations	7,433	46,866	7,433	88,336
Cash repayments / receipts	(8,555)	(16,197)	(18,783)	(23,008)
Balance at the end of the period	256,397	251,260	256,397	251,260
Amount of total (losses) gains included in earnings attributable to assets still held at period end	3,186	3,742	6,973	7,157
CMBS | Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	15,472	96,724	31,546	212,981
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(2,343)	1,349	(3,686)	2,316
Purchases / Originations		24,403		57,576
Sales	(700)	(1,269)	(11,134)	(1,269)
Cash repayments / receipts	(1,322)	(7,142)	(7,088)	(19,445)
Consolidations of VIEs				(138,342)
Deconsolidations of VIEs	2,741	275	4,210	523
Balance at the end of the period	13,848	114,340	13,848	114,340
Amount of total (losses) gains included in earnings attributable to assets still held at period end	396	2,208	228	3,778
Domestic servicing rights | Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	46,649	95,492	55,082	119,698
Impact of ASU 2015-02 Adoption				(17,467)
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(8,001)	(12,191)	(16,434)	(18,930)
Balance at the end of the period	38,648	83,301	38,648	83,301
Amount of total (losses) gains included in earnings attributable to assets still held at period end	(8,001)	(12,191)	(16,434)	(18,930)
VIE Assets | Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	60,185,851	85,115,662	67,123,261	76,675,689
Impact of ASU 2015-02 Adoption				17,467
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(5,702,684)	(4,250,779)	(12,239,909)	(8,340,280)
Consolidations of VIEs		1,746,946	1,127,952	16,850,221
Deconsolidations of VIEs	(580,452)	(2,535,712)	(2,108,589)	(5,126,980)
Balance at the end of the period	53,902,715	80,076,117	53,902,715	80,076,117
Amount of total (losses) gains included in earnings attributable to assets still held at period end	$ (5,702,684)	$ (4,250,779)	$ (12,239,909)	$ (8,340,280)