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SECURITIES - Summary of Residential Securities and CMBS (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($)
Debt Securities, Available-For-Sale [Roll Forward]
Beginning balance January 1, 2021	$ 75,652,396
Purchases	21,551,356
Sales and transfers	(11,631,908)
Principal paydowns	(18,741,496)
(Amortization) / accretion	(760,062)
Fair value adjustment	(2,414,612)
Ending balance December 31, 2021	63,655,674
Agency Securities
Debt Securities, Available-For-Sale [Roll Forward]
Beginning balance January 1, 2021	74,067,059
Purchases	18,887,983
Sales and transfers	(11,392,003)
Principal paydowns	(17,860,666)
(Amortization) / accretion	(761,838)
Fair value adjustment	(2,414,930)
Ending balance December 31, 2021	60,525,605
Residential Credit Securities
Debt Securities, Available-For-Sale [Roll Forward]
Beginning balance January 1, 2021	1,504,595
Purchases	2,129,147
Sales and transfers	(156,130)
Principal paydowns	(880,649)
(Amortization) / accretion	1,478
Fair value adjustment	1,123
Ending balance December 31, 2021	2,599,564
Commercial mortgage-backed securities
Debt Securities, Available-For-Sale [Roll Forward]
Beginning balance January 1, 2021	80,742
Purchases	534,226
Sales and transfers	(83,775)
Principal paydowns	(181)
(Amortization) / accretion	298
Fair value adjustment	(805)
Ending balance December 31, 2021	$ 530,505

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