Fair Value - Level III (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Total realized and unrealized gains (losses):
Included in earnings: Net accretion	$ 2,783	$ 2,755
Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	61,317,478	52,931,064
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(3,371,299)	338,506
Included in earnings: Net accretion	2,661	2,503
Included in OCI	(15,048)	(387)
Purchases / Originations	746,880	740,296
Sales	(759,686)	(564,930)
Issuances	(24,376)	(33,678)
Cash repayments / receipts	(83,233)	(26,392)
Transfers into Level III	(101,265)	(665,392)
Transfers out of Level III	1,090,325	136,592
Consolidations of VIEs	2,406,327	3,176,756
Deconsolidations of VIEs		(1,986)
Balance at the end of the period	61,208,764	56,032,952
Amount of total (losses) gains included in earnings attributable to assets still held at period end	(3,397,959)	332,640
Amount of total (losses) gains included in OCI attributable to assets still held at period end	(15,048)
Loans held-for-sale \| Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	1,436,194	671,282
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(16,134)	11,266
Purchases / Originations	746,880	740,296
Sales	(751,746)	(561,702)
Cash repayments / receipts	(67,397)	(19,455)
Balance at the end of the period	1,347,797	841,687
Amount of total (losses) gains included in earnings attributable to assets still held at period end	(39,070)	3,169
RMBS \| Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	189,576	209,079
Total realized and unrealized gains (losses):
Included in earnings: Net accretion	2,661	2,503
Included in OCI	(15,048)	(387)
Cash repayments / receipts	(6,549)	(6,360)
Balance at the end of the period	170,640	204,835
Amount of total (losses) gains included in earnings attributable to assets still held at period end	2,661	2,503
Amount of total (losses) gains included in OCI attributable to assets still held at period end	(15,048)
CMBS \| Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	25,008	25,228
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	5,738	(295)
Sales	(7,940)	(3,228)
Cash repayments / receipts	(371)	(188)
Transfers into Level III		5,350
Deconsolidations of VIEs		11,468
Balance at the end of the period	22,435	38,335
Amount of total (losses) gains included in earnings attributable to assets still held at period end	(647)	(567)
Domestic Servicing Rights \| Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	16,917	20,557
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(393)	(767)
Balance at the end of the period	16,524	19,790
Amount of total (losses) gains included in earnings attributable to assets still held at period end	(393)	(767)
VIE Assets \| Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	62,187,175	53,446,364
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(3,506,792)	294,345
Consolidations of VIEs	2,477,422	3,280,065
Deconsolidations of VIEs		(45,910)
Balance at the end of the period	61,157,805	56,974,864
Amount of total (losses) gains included in earnings attributable to assets still held at period end	(3,506,792)	294,345
VIE liabilities \| Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	(2,537,392)	(1,441,446)
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	146,282	33,957
Issuances	(24,376)	(33,678)
Cash repayments / receipts	(8,916)	(389)
Transfers into Level III	(101,265)	(670,742)
Transfers out of Level III	1,090,325	136,592
Consolidations of VIEs	(71,095)	(103,309)
Deconsolidations of VIEs		32,456
Balance at the end of the period	(1,506,437)	(2,046,559)
Amount of total (losses) gains included in earnings attributable to assets still held at period end	$ 146,282	$ 33,957

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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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Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input, still held at the end of 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 (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

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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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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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