Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
AFS securities
Amortized Cost	$ 75,160	$ 74,227
Gross Unrealized Gains	2,656	677
Gross Unrealized Losses	11	177
AFS securities, Fair Value	77,805	74,727
U.S. Treasury
AFS securities
Amortized Cost	2,220	2,275
Gross Unrealized Gains	40	7
Gross Unrealized Losses	0	6
AFS securities, Fair Value	2,260	2,276
US Government-sponsored Enterprises Debt Securities
AFS securities
Amortized Cost	1,844	1,847
Gross Unrealized Gains	91	34
Gross Unrealized Losses	0	0
AFS securities, Fair Value	1,935	1,881
Agency MBS \| Residential Mortgage Backed Securities
AFS securities
Amortized Cost	69,141	67,983
Gross Unrealized Gains	2,412	411
Gross Unrealized Losses	6	158
AFS securities, Fair Value	71,547	68,236
Agency MBS \| Commercial Mortgage Backed Securities
AFS securities
Amortized Cost	1,420	1,335
Gross Unrealized Gains	71	13
Gross Unrealized Losses	0	7
AFS securities, Fair Value	1,491	1,341
States and political subdivisions
AFS securities
Amortized Cost	499	557
Gross Unrealized Gains	42	34
Gross Unrealized Losses	4	6
AFS securities, Fair Value	537	585
Non-agency MBS
AFS securities
Amortized Cost		190
Gross Unrealized Gains		178
Gross Unrealized Losses		0
AFS securities, Fair Value		368
Other
AFS securities
Amortized Cost	36	40
Gross Unrealized Gains	0	0
Gross Unrealized Losses	1	0
AFS securities, Fair Value	$ 35	$ 40

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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Amortized cost 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 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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