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Investment Securities - Investment Available for Sale (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 92,927	$ 92,995
Allowance for Credit Losses	(3)	(4)
Gross Unrealized Gains	209	148
Gross Unrealized Losses	(8,771)	(10,126)
Fair Value	84,362	83,013
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,222	6,114
Allowance for Credit Losses	0	0
Gross Unrealized Gains	5	5
Gross Unrealized Losses	(6)	(9)
Fair Value	6,221	6,110
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	74,163	74,177
Allowance for Credit Losses	0	0
Gross Unrealized Gains	105	57
Gross Unrealized Losses	(8,273)	(9,527)
Fair Value	65,995	64,707
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	557	567
Allowance for Credit Losses	(3)	(4)
Gross Unrealized Gains	71	64
Gross Unrealized Losses	(4)	(6)
Fair Value	621	621
Total RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	74,720	74,744
Allowance for Credit Losses	(3)	(4)
Gross Unrealized Gains	176	121
Gross Unrealized Losses	(8,277)	(9,533)
Fair Value	66,616	65,328
Agency CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,437	8,389
Allowance for Credit Losses	0	0
Gross Unrealized Gains	24	17
Gross Unrealized Losses	(487)	(581)
Fair Value	7,974	7,825
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,548	3,748
Allowance for Credit Losses	0	0
Gross Unrealized Gains	4	5
Gross Unrealized Losses	(1)	(3)
Fair Value	3,551	3,750
Asset-backed Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 1,800	$ 2,000

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