Investment Securities - Amortized Cost, Gross Unrealized Gains and Losses, and Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
AFS securities
Total	$ 74,227	$ 25,689
Gross Unrealized Gains	677	247
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	177	898
AFS securities, Fair Value	74,727	25,038
HTM securities
HTM securities, Amortized Cost	0	20,552
Gross Unrealized Gains		31
Gross Unrealized Losses		536
HTM securities, Fair Value		20,047
U.S. Treasury
AFS securities
Total	2,275	3,503
Gross Unrealized Gains	7	22
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	6	84
AFS securities, Fair Value	2,276	3,441
HTM securities
HTM securities, Amortized Cost		1,099
Gross Unrealized Gains		0
Gross Unrealized Losses		6
HTM securities, Fair Value		1,093
US Government-sponsored Enterprises Debt Securities [Member]
AFS securities
Total	1,847	209
Gross Unrealized Gains	34	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	9
AFS securities, Fair Value	1,881	200
HTM securities
HTM securities, Amortized Cost		2,199
Gross Unrealized Gains		4
Gross Unrealized Losses		43
HTM securities, Fair Value		2,160
Agency MBS
HTM securities
HTM securities, Amortized Cost		17,248
Gross Unrealized Gains		27
Gross Unrealized Losses		487
HTM securities, Fair Value		16,788
Agency MBS \| Commercial Mortgage Backed Securities
AFS securities
Total	1,335	757
Gross Unrealized Gains	13	0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	7	28
AFS securities, Fair Value	1,341	729
Agency MBS \| Residential Mortgage Backed Securities
AFS securities
Total	67,983	20,170
Gross Unrealized Gains	411	15
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	158	759
AFS securities, Fair Value	68,236	19,426
States and political subdivisions
AFS securities
Total	557	694
Gross Unrealized Gains	34	25
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	6	18
AFS securities, Fair Value	585	701
HTM securities
HTM securities, Amortized Cost		5
Gross Unrealized Gains		0
Gross Unrealized Losses		0
HTM securities, Fair Value		5
Non-agency MBS
AFS securities
Total	190	321
Gross Unrealized Gains	178	184
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
AFS securities, Fair Value	368	505
Other
AFS securities
Total	40	35
Gross Unrealized Gains	0	1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
AFS securities, Fair Value	$ 40	36
HTM securities
HTM securities, Amortized Cost		1
Gross Unrealized Gains		0
Gross Unrealized Losses		0
HTM securities, Fair Value		$ 1

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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