Investment Securities - Investment Available for Sale (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 88,459	$ 88,063
Allowance for Credit Losses	(4)	(4)
Gross Unrealized Gains	186	214
Gross Unrealized Losses	(10,243)	(9,156)
Fair Value	78,398	79,117
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,764	5,330
Allowance for Credit Losses	0	0
Gross Unrealized Gains	3	1
Gross Unrealized Losses	(39)	(49)
Fair Value	5,728	5,282
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	71,153	71,294
Allowance for Credit Losses	0	0
Gross Unrealized Gains	74	104
Gross Unrealized Losses	(9,506)	(8,450)
Fair Value	61,721	62,948
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	600	610
Allowance for Credit Losses	(4)	(4)
Gross Unrealized Gains	86	89
Gross Unrealized Losses	(5)	(5)
Fair Value	677	690
Total RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	71,753	71,904
Allowance for Credit Losses	(4)	(4)
Gross Unrealized Gains	160	193
Gross Unrealized Losses	(9,511)	(8,455)
Fair Value	62,398	63,638
Agency CMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	8,867	8,961
Allowance for Credit Losses	0	0
Gross Unrealized Gains	19	14
Gross Unrealized Losses	(693)	(652)
Fair Value	8,193	8,323
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,075	1,868
Allowance for Credit Losses	0	0
Gross Unrealized Gains	4	6
Gross Unrealized Losses	0	0
Fair Value	2,079	1,874
Asset-backed Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 1,600	$ 1,400

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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