Investment Securities - Investment Available for Sale (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 100,336	$ 97,569
Allowance for Credit Losses	(1)	(1)
Gross Unrealized Gains	2,005	2,997
Gross Unrealized Losses	(574)	(120)
Fair Value	101,766	100,445
Accrued interest receivable	221	230
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9,211	9,302
Allowance for Credit Losses	0	0
Gross Unrealized Gains	20	16
Gross Unrealized Losses	0	0
Fair Value	9,231	9,318
RMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	76,318	73,248
Allowance for Credit Losses	0	0
Gross Unrealized Gains	1,433	2,326
Gross Unrealized Losses	(545)	(108)
Fair Value	77,206	75,466
RMBS, Non-agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	908	1,035
Allowance for Credit Losses	(1)	(1)
Gross Unrealized Gains	209	204
Gross Unrealized Losses	0	(1)
Fair Value	1,116	1,237
RMBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	77,226	74,283
Allowance for Credit Losses	(1)	(1)
Gross Unrealized Gains	1,642	2,530
Gross Unrealized Losses	(545)	(109)
Fair Value	78,322	76,703
CMBS, Agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	10,781	11,298
Allowance for Credit Losses	0	0
Gross Unrealized Gains	335	448
Gross Unrealized Losses	(29)	(11)
Fair Value	11,087	11,735
Other securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	3,118	2,686
Allowance for Credit Losses	0	0
Gross Unrealized Gains	8	3
Gross Unrealized Losses	0	0
Fair Value	3,126	2,689
Asset-backed Securities
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 2,300	$ 1,800

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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Amount of allowance for credit loss 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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