Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
AFS securities
Amortized Cost	$ 155,088	$ 118,618
Gross Unrealized Gains	755	2,196
Gross Unrealized Losses	2,720	26
AFS securities, Fair Value	153,123	120,788
HTM securities	1,495	0
HTM securities:
Amortized Cost	1,494	0
Gross Unrealized Gains	1
Gross Unrealized Losses	0
U.S. Treasury
AFS securities
Amortized Cost	9,892	1,721
Gross Unrealized Gains	9	25
Gross Unrealized Losses	106	0
AFS securities, Fair Value	9,795	1,746
GSE
AFS securities
Amortized Cost	1,667	1,840
Gross Unrealized Gains	33	77
Gross Unrealized Losses	2	0
AFS securities, Fair Value	1,698	1,917
Agency MBS \| Agency MBS - residential
AFS securities
Amortized Cost	135,886	111,589
Gross Unrealized Gains	656	1,975
Gross Unrealized Losses	2,500	23
AFS securities, Fair Value	134,042	113,541
Agency MBS \| Commercial Mortgage Backed Securities
AFS securities
Amortized Cost	2,928	2,987
Gross Unrealized Gains	18	72
Gross Unrealized Losses	64	2
AFS securities, Fair Value	2,882	3,057
States and political subdivisions
AFS securities
Amortized Cost	382	447
Gross Unrealized Gains	39	47
Gross Unrealized Losses	1	1
AFS securities, Fair Value	420	493
Non-agency MBS
AFS securities
Amortized Cost	4,305
Gross Unrealized Gains	0
Gross Unrealized Losses	47
AFS securities, Fair Value	4,258
Other
AFS securities
Amortized Cost	28	34
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
AFS securities, Fair Value	$ 28	$ 34

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, before tax, of unrealized loss 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 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, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

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