SECURITIES - Summary of Residential Securities and CMBS (Details) $ in Thousands	9 Months Ended
Sep. 30, 2020 USD ($)
Debt Securities, Available-For-Sale [Roll Forward]
Beginning balance	$ 114,833,580
Purchases	25,679,591
Sales and transfers	(50,283,998)
Principal paydowns	(14,359,102)
(Amortization) / accretion	(1,135,109)
Fair value adjustment	1,364,023
Ending balance	76,098,985
Residential Securities
Debt Securities, Available-For-Sale [Roll Forward]
Beginning balance	114,560,557
Purchases	25,679,591
Sales and transfers	(50,079,936)
Principal paydowns	(14,354,169)
(Amortization) / accretion	(1,135,486)
Fair value adjustment	1,373,750
Ending balance	76,044,307
Commercial Securities
Debt Securities, Available-For-Sale [Roll Forward]
Beginning balance	273,023
Purchases	0
Sales and transfers	(204,062)
Principal paydowns	(4,933)
(Amortization) / accretion	377
Fair value adjustment	(9,727)
Ending balance	$ 54,678

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Debt Securities, Available-For-Sale [Roll Forward]

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount after tax and reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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