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Investment Securities - Investment Available for Sale (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 90,771	$ 88,063
Allowance for Credit Losses	(3)	(4)
Gross Unrealized Gains	343	214
Gross Unrealized Losses	(7,611)	(9,156)
Fair Value	83,500	79,117
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	6,035	5,330
Allowance for Credit Losses	0	0
Gross Unrealized Gains	10	1
Gross Unrealized Losses	(13)	(49)
Fair Value	6,032	5,282
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	72,576	71,294
Allowance for Credit Losses	0	0
Gross Unrealized Gains	205	104
Gross Unrealized Losses	(7,130)	(8,450)
Fair Value	65,651	62,948
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	576	610
Allowance for Credit Losses	(3)	(4)
Gross Unrealized Gains	86	89
Gross Unrealized Losses	(3)	(5)
Fair Value	656	690
Total RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	73,152	71,904
Allowance for Credit Losses	(3)	(4)
Gross Unrealized Gains	291	193
Gross Unrealized Losses	(7,133)	(8,455)
Fair Value	66,307	63,638
Agency CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,613	8,961
Allowance for Credit Losses	0	0
Gross Unrealized Gains	35	14
Gross Unrealized Losses	(465)	(652)
Fair Value	8,183	8,323
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,971	1,868
Allowance for Credit Losses	0	0
Gross Unrealized Gains	7	6
Gross Unrealized Losses	0	0
Fair Value	2,978	1,874
Asset-backed Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 2,400	$ 1,400

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