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Investment Securities - Investment Available for Sale (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 96,939	$ 92,995
Allowance for Credit Losses	(3)	(4)
Gross Unrealized Gains	361	148
Gross Unrealized Losses	(7,564)	(10,126)
Fair Value	89,733	83,013
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,613	6,114
Allowance for Credit Losses	0	0
Gross Unrealized Gains	28	5
Gross Unrealized Losses	(4)	(9)
Fair Value	8,637	6,110
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	75,246	74,177
Allowance for Credit Losses	0	0
Gross Unrealized Gains	218	57
Gross Unrealized Losses	(7,167)	(9,527)
Fair Value	68,297	64,707
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	536	567
Allowance for Credit Losses	(3)	(4)
Gross Unrealized Gains	72	64
Gross Unrealized Losses	(3)	(6)
Fair Value	602	621
Total RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	75,782	74,744
Allowance for Credit Losses	(3)	(4)
Gross Unrealized Gains	290	121
Gross Unrealized Losses	(7,170)	(9,533)
Fair Value	68,899	65,328
Agency CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,795	8,389
Allowance for Credit Losses	0	0
Gross Unrealized Gains	35	17
Gross Unrealized Losses	(390)	(581)
Fair Value	8,440	7,825
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,749	3,748
Allowance for Credit Losses	0	0
Gross Unrealized Gains	8	5
Gross Unrealized Losses	0	(3)
Fair Value	3,757	3,750
Asset-backed Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 1,800	$ 2,000

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