Fair Value - Level III (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Total realized and unrealized gains (losses):
Included in earnings: OTTI	$ (728)		$ (1,056)
Included in earnings: Net accretion	16,527	$ 24,556	25,023
Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	74,836,009	103,988,001
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(23,730,997)	(31,336,587)
Included in earnings: Net accretion	15,479	20,625
Included in OCI	7,622	(18,573)
Purchases / Originations	1,826,577	1,863,532
Sales	(1,903,105)	(2,106,626)
Issuances	(35,728)	(9,132)
Cash repayments / receipts	(50,196)	168,096
Transfers into Level III	(1,101,416)	(2,920,033)
Transfers out of Level III	268,915	1,290,497
Consolidations of VIEs	20,478,776	11,663,104
Deconsolidations of VIEs	(5,670,222)	(7,766,895)
Balance at the end of the period	64,941,714	74,836,009	103,988,001
Amount of total (losses) gains included in earnings attributable to assets still held at period end	(23,789,339)	(31,379,394)
VIE liabilities \| Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	(2,552,448)	(4,893,120)
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	1,385,108	3,980,376
Issuances	(35,728)	(9,132)
Cash repayments / receipts	53,107	304,816
Transfers into Level III	(1,101,416)	(2,920,033)
Transfers out of Level III	268,915	1,290,497
Consolidations of VIEs	(648,352)	(363,008)
Deconsolidations of VIEs	45,445	57,156
Balance at the end of the period	(2,585,369)	(2,552,448)	(4,893,120)
Amount of total (losses) gains included in earnings attributable to assets still held at period end	1,385,108	3,980,376
Loans held-for-sale \| Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	203,865	391,620
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	74,251	64,320
Purchases / Originations	1,670,966	1,848,879
Sales	(1,884,380)	(2,100,216)
Cash repayments / receipts	(1,423)	(738)
Balance at the end of the period	63,279	203,865	391,620
Amount of total (losses) gains included in earnings attributable to assets still held at period end	214	155
RMBS \| Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	176,224	207,053
Total realized and unrealized gains (losses):
Included in earnings: Net accretion	15,479	20,625
Included in OCI	7,622	(16,210)
Purchases / Originations	98,035
Cash repayments / receipts	(43,445)	(35,244)
Balance at the end of the period	253,915	176,224	207,053
Amount of total (losses) gains included in earnings attributable to assets still held at period end	15,479	15,131
CMBS \| Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	212,981	334,080
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(1,421)	(3,093)
Included in OCI		(2,363)
Purchases / Originations	57,576	14,653
Sales	(18,725)	(6,410)
Cash repayments / receipts	(58,435)	(100,738)
Consolidations of VIEs	(162,745)	(24,309)
Deconsolidations of VIEs	2,315	1,161
Balance at the end of the period	31,546	212,981	334,080
Amount of total (losses) gains included in earnings attributable to assets still held at period end	(1,205)	3,134
Domestic servicing rights \| Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	119,698	132,303
Impact of ASU 2015-02 Adoption	(17,467)
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(47,149)	(12,605)
Balance at the end of the period	55,082	119,698	132,303
Amount of total (losses) gains included in earnings attributable to assets still held at period end	(47,149)	(12,605)
VIE Assets \| Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	76,675,689	107,816,065
Impact of ASU 2015-02 Adoption	17,467
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(25,141,786)	(35,365,585)
Consolidations of VIEs	21,289,873	12,050,421
Deconsolidations of VIEs	(5,717,982)	(7,825,212)
Balance at the end of the period	67,123,261	76,675,689	$ 107,816,065
Amount of total (losses) gains included in earnings attributable to assets still held at period end	$ (25,141,786)	$ (35,365,585)

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Amount of adjustment for adoption of accounting pronouncement recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Represents the change due to the consolidations of Variable Interest Entity (VIE) that have taken place during the period in relation to the assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

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This item represents the amount of the total realized and unrealized gains or losses for the period which are included in the statement of income (or changes in net assets) in change in fair value; the fair value of which assets was or is measured on a recurring basis using significant unobservable inputs (Level 3).

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Amount of gain (loss) recognized on the income statement for a financial instrument classified as an asset measured using unobservable inputs, still held at the end of the period.

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The sum of the periodic adjustments of the differences between securities' face values and purchase prices that are charged against earnings. This is called accretion if the security was purchased at a discount and amortization if it was purchased at premium. As a noncash item, this element is an adjustment to net income when calculating cash provided by or used in operations using the indirect method.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of issuances of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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The amount of other than temporary impairment losses on investments in debt and equity securities categorized as Available-for-sale which have been recognized in earnings during the period. Such impairment losses consist of other than temporary impairments (OTTI) on equity securities, credit losses on investments in debt securities, and when the entity intends to sell an impaired debt security or it is more likely than not that the entity will be required to sell the impaired debt security before recovery of its amortized cost basis.

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