SECURITIES - Summary of Residential Securities and CMBS (Details) $ in Thousands	3 Months Ended
Mar. 31, 2022 USD ($)
Debt Securities, Available-For-Sale [Roll Forward]
Beginning balance January 1, 2022	$ 63,655,674
Purchases	6,533,134
Sales and transfers	(2,930,436)
Principal paydowns	(3,043,386)
(Amortization) / accretion	25,550
Fair value adjustment	(3,512,899)
Ending balance March 31, 2022	60,727,637
Agency Securities
Debt Securities, Available-For-Sale [Roll Forward]
Beginning balance January 1, 2022	60,525,605
Purchases	6,160,670
Sales and transfers	(2,583,651)
Principal paydowns	(2,910,094)
(Amortization) / accretion	24,656
Fair value adjustment	(3,430,045)
Ending balance March 31, 2022	57,787,141
Residential Credit Securities
Debt Securities, Available-For-Sale [Roll Forward]
Beginning balance January 1, 2022	2,599,564
Purchases	372,464
Sales and transfers	(177,561)
Principal paydowns	(132,519)
(Amortization) / accretion	890
Fair value adjustment	(79,696)
Ending balance March 31, 2022	2,583,142
Commercial Securities
Debt Securities, Available-For-Sale [Roll Forward]
Beginning balance January 1, 2022	530,505
Purchases	0
Sales and transfers	(169,224)
Principal paydowns	(773)
(Amortization) / accretion	4
Fair value adjustment	(3,158)
Ending balance March 31, 2022	$ 357,354

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