Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
AFS securities
Amortized Cost	$ 75,650	$ 74,227
Gross Unrealized Gains	2,794	677
Gross Unrealized Losses	46	177
AFS securities, Fair Value	78,398	74,727
U.S. Treasury
AFS securities
Amortized Cost	2,272	2,275
Gross Unrealized Gains	47	7
Gross Unrealized Losses	0	6
AFS securities, Fair Value	2,319	2,276
US Government-sponsored Enterprises Debt Securities [Member]
AFS securities
Amortized Cost	1,846	1,847
Gross Unrealized Gains	87	34
Gross Unrealized Losses	0	0
AFS securities, Fair Value	1,933	1,881
Agency MBS \| Residential Mortgage Backed Securities
AFS securities
Amortized Cost	69,307	67,983
Gross Unrealized Gains	2,468	411
Gross Unrealized Losses	22	158
AFS securities, Fair Value	71,753	68,236
Agency MBS \| Commercial Mortgage Backed Securities
AFS securities
Amortized Cost	1,489	1,335
Gross Unrealized Gains	31	13
Gross Unrealized Losses	1	7
AFS securities, Fair Value	1,519	1,341
States and political subdivisions
AFS securities
Amortized Cost	513	557
Gross Unrealized Gains	34	34
Gross Unrealized Losses	8	6
AFS securities, Fair Value	539	585
Non-agency MBS
AFS securities
Amortized Cost	185	190
Gross Unrealized Gains	127	178
Gross Unrealized Losses	14	0
AFS securities, Fair Value	298	368
Other
AFS securities
Amortized Cost	38	40
Gross Unrealized Gains	0	0
Gross Unrealized Losses	1	0
AFS securities, Fair Value	$ 37	$ 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).

+ References

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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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