Fair Value - Level III (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Total realized and unrealized gains (losses):
Included in earnings: Net accretion			$ 6,123	$ 7,857
Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	$ 61,208,764	$ 56,032,952	61,317,478	52,931,064
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	2,440,491	152,072	(930,808)	490,578
Included in earnings: Net accretion	2,673	2,535	5,334	5,038
Included in OCI	6,982	(79)	(8,066)	(466)
Purchases / Originations	140,700	911,938	887,580	1,652,234
Sales	(589,694)	(367,795)	(1,349,380)	(932,725)
Issuances		(25,045)	(24,376)	(58,723)
Cash repayments / receipts	(45,191)	(50,773)	(128,424)	(77,165)
Transfers into Level III	(655,942)	(594,399)	(757,207)	(1,259,791)
Transfers out of Level III	41,880	294,227	1,132,205	430,819
Consolidations of VIEs	599,935	819,529	3,006,262	3,996,285
Deconsolidations of VIEs		(255,129)		(257,115)
Balance at the end of the period	63,150,598	56,920,033	63,150,598	56,920,033
Amount of total (losses) gains included in earnings attributable to assets still held at period end	2,429,063	137,657	(948,587)	466,726
Amount of total (losses) gains included in OCI attributable to assets still held at period end	6,982		(8,066)
Level III \| Loans held-for-sale
Changes in financial assets classified as Level III
Balance at the beginning of the period	1,347,797	841,687	1,436,194	671,282
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	34,450	21,891	18,316	33,157
Purchases / Originations	140,700	911,938	887,580	1,652,234
Sales	(589,694)	(367,045)	(1,341,440)	(928,747)
Cash repayments / receipts	(38,640)	(36,073)	(106,037)	(55,528)
Balance at the end of the period	894,613	1,372,398	894,613	1,372,398
Amount of total (losses) gains included in earnings attributable to assets still held at period end	20,349	5,547	1,589	5,145
Level III \| RMBS
Changes in financial assets classified as Level III
Balance at the beginning of the period	170,640	204,835	189,576	209,079
Total realized and unrealized gains (losses):
Included in earnings: Net accretion	2,673	2,535	5,334	5,038
Included in OCI	6,982	(79)	(8,066)	(466)
Cash repayments / receipts	(6,014)	(6,417)	(12,563)	(12,777)
Balance at the end of the period	174,281	200,874	174,281	200,874
Amount of total (losses) gains included in earnings attributable to assets still held at period end	2,673	2,535	5,334	5,038
Amount of total (losses) gains included in OCI attributable to assets still held at period end	6,982		(8,066)
Level III \| CMBS
Changes in financial assets classified as Level III
Balance at the beginning of the period	22,435	38,335	25,008	25,228
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(351)	1,016	5,387	721
Sales		(750)	(7,940)	(3,978)
Cash repayments / receipts	(193)	(5,402)	(564)	(5,590)
Transfers into Level III				5,350
Deconsolidations of VIEs		1,084		12,552
Balance at the end of the period	21,891	34,283	21,891	34,283
Amount of total (losses) gains included in earnings attributable to assets still held at period end	(351)	410	(999)	(157)
Level III \| Domestic Servicing Rights
Changes in financial assets classified as Level III
Balance at the beginning of the period	16,524	19,790	16,917	20,557
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(2,569)	(916)	(2,962)	(1,683)
Balance at the end of the period	13,955	18,874	13,955	18,874
Amount of total (losses) gains included in earnings attributable to assets still held at period end	(2,569)	(916)	(2,962)	(1,683)
Level III \| VIE Assets
Changes in financial assets classified as Level III
Balance at the beginning of the period	61,157,805	56,974,864	62,187,175	53,446,364
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	2,417,647	126,589	(1,089,145)	420,934
Consolidations of VIEs	599,935	824,070	3,077,357	4,104,135
Deconsolidations of VIEs		(257,917)		(303,827)
Balance at the end of the period	64,175,387	57,667,606	64,175,387	57,667,606
Amount of total (losses) gains included in earnings attributable to assets still held at period end	2,417,647	126,589	(1,089,145)	420,934
Level III \| VIE liabilities
Changes in financial assets classified as Level III
Balance at the beginning of the period	(1,506,437)	(2,046,559)	(2,537,392)	(1,441,446)
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(8,686)	3,492	137,596	37,449
Issuances		(25,045)	(24,376)	(58,723)
Cash repayments / receipts	(344)	(2,881)	(9,260)	(3,270)
Transfers into Level III	(655,942)	(594,399)	(757,207)	(1,265,141)
Transfers out of Level III	41,880	294,227	1,132,205	430,819
Consolidations of VIEs		(4,541)	(71,095)	(107,850)
Deconsolidations of VIEs		1,704		34,160
Balance at the end of the period	(2,129,529)	(2,374,002)	(2,129,529)	(2,374,002)
Amount of total (losses) gains included in earnings attributable to assets still held at period end	$ (8,686)	$ 3,492	$ 137,596	$ 37,449

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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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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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