SECURITIES - Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2022 USD ($) security	Dec. 31, 2021 USD ($) security
Unrealized Loss Position For:
Estimated Fair Value	$ 60,727,637	$ 63,655,674
Gross Unrealized Losses	(2,934,524)	(673,774)
Agency Mortgage-Backed Securities
Unrealized Loss Position For:
Estimated Fair Value	49,217,048	23,211,971
Gross Unrealized Losses	$ (2,640,148)	$ (486,024)
Number of Securities | security	2,139	590
Agency Mortgage-Backed Securities | Less than 12 months
Unrealized Loss Position For:
Estimated Fair Value	$ 37,098,530	$ 22,828,156
Gross Unrealized Losses	$ (1,402,053)	$ (475,064)
Number of Securities | security	1,838	571
Agency Mortgage-Backed Securities | 12 Months or more
Unrealized Loss Position For:
Estimated Fair Value	$ 12,118,518	$ 383,815
Gross Unrealized Losses	$ (1,238,095)	$ (10,960)
Number of Securities | security	301	19