Fair Value - Level III (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Total realized and unrealized gains (losses):
Included in earnings: Net accretion	$ 3,476	$ 2,783
Level III
Changes in financial assets classified as Level III
Balance at the beginning of the period	63,441,439	61,317,478
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(2,208,812)	(3,371,299)
Included in earnings: Net accretion	2,606	2,661
Included in OCI	(2,403)	(15,048)
Purchases / Originations	375,270	746,880
Sales	(571,927)	(759,686)
Issuances	(11,604)	(24,376)
Cash repayments / receipts	(62,032)	(83,233)
Transfers into Level III	(409,267)	(101,265)
Transfers out of Level III	148,775	1,090,325
Consolidations of VIEs	393,373	2,406,327
Balance at the end of the period	61,095,418	61,208,764
Amount of unrealized gains (losses) included in earnings attributable to assets still held at period end	(2,204,436)	(3,397,959)
Amount of unrealized gains (losses) included in OCI attributable to assets still held at period end	(2,403)	(15,048)
Level III \| Loans held-for-sale
Changes in financial assets classified as Level III
Balance at the beginning of the period	1,022,979	1,436,194
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(9,478)	(16,134)
Purchases / Originations	375,270	746,880
Sales	(571,927)	(751,746)
Cash repayments / receipts	(53,071)	(67,397)
Balance at the end of the period	763,773	1,347,797
Amount of unrealized gains (losses) included in earnings attributable to assets still held at period end	(7,708)	(39,070)
Level III \| RMBS
Changes in financial assets classified as Level III
Balance at the beginning of the period	167,349	189,576
Total realized and unrealized gains (losses):
Included in earnings: Net accretion	2,606	2,661
Included in OCI	(2,403)	(15,048)
Cash repayments / receipts	(7,251)	(6,549)
Balance at the end of the period	160,301	170,640
Amount of unrealized gains (losses) included in earnings attributable to assets still held at period end	2,606	2,661
Amount of unrealized gains (losses) included in OCI attributable to assets still held at period end	(2,403)	(15,048)
Level III \| CMBS
Changes in financial assets classified as Level III
Balance at the beginning of the period	19,457	25,008
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	372	5,738
Sales		(7,940)
Cash repayments / receipts	(573)	(371)
Balance at the end of the period	19,256	22,435
Amount of unrealized gains (losses) included in earnings attributable to assets still held at period end	372	(647)
Level III \| Domestic Servicing Rights
Changes in financial assets classified as Level III
Balance at the beginning of the period	13,202	16,917
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(796)	(393)
Balance at the end of the period	12,406	16,524
Amount of unrealized gains (losses) included in earnings attributable to assets still held at period end	(796)	(393)
Level III \| VIE Assets
Changes in financial assets classified as Level III
Balance at the beginning of the period	64,238,328	62,187,175
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	(2,264,591)	(3,506,792)
Consolidations of VIEs	393,373	2,477,422
Balance at the end of the period	62,367,110	61,157,805
Amount of unrealized gains (losses) included in earnings attributable to assets still held at period end	(2,264,591)	(3,506,792)
Level III \| VIE liabilities
Changes in financial assets classified as Level III
Balance at the beginning of the period	(2,019,876)	(2,537,392)
Total realized and unrealized gains (losses):
Included in earnings: Change in fair value / gain on sale	65,681	146,282
Issuances	(11,604)	(24,376)
Cash repayments / receipts	(1,137)	(8,916)
Transfers into Level III	(409,267)	(101,265)
Transfers out of Level III	148,775	1,090,325
Consolidations of VIEs		(71,095)
Balance at the end of the period	(2,227,428)	(1,506,437)
Amount of unrealized gains (losses) included in earnings attributable to assets still held at period end	$ 65,681	$ 146,282

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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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