Securities - Details of Securities (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
SECURITIES AVAILABLE FOR SALE
Amortized Cost	$ 22,750	$ 21,692
Gross Unrealized Gains	851	266
Gross Unrealized Losses	1	115
Fair Value	23,600	21,843
HELD-TO-MATURITY SECURITIES
Amortized Cost	9,075	10,067
Gross Unrealized Gains	445	107
Gross Unrealized Losses	0	58
Fair Value	9,520	10,116
Accrued interest	225	244
U.S. Treasury, agencies and corporations
SECURITIES AVAILABLE FOR SALE
Amortized Cost	3,465	334
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	3,465	334
States and political subdivisions
SECURITIES AVAILABLE FOR SALE
Amortized Cost	3	4
Gross Unrealized Gains	1	0
Gross Unrealized Losses	0	0
Fair Value	4	4
Collateralized mortgage Obligations
SECURITIES AVAILABLE FOR SALE
Amortized Cost	11,600	12,772
Gross Unrealized Gains	348	82
Gross Unrealized Losses	1	71
Fair Value	11,947	12,783
HELD-TO-MATURITY SECURITIES
Amortized Cost	4,886	5,692
Gross Unrealized Gains	151	23
Gross Unrealized Losses	0	49
Fair Value	5,037	5,666
Agency residential mortgage-backed securities
SECURITIES AVAILABLE FOR SALE
Amortized Cost	1,373	1,677
Gross Unrealized Gains	72	41
Gross Unrealized Losses	0	4
Fair Value	1,445	1,714
HELD-TO-MATURITY SECURITIES
Amortized Cost	359	409
Gross Unrealized Gains	16	6
Gross Unrealized Losses	0	0
Fair Value	375	415
Asset-backed securities
HELD-TO-MATURITY SECURITIES
Amortized Cost	10	11
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	10	11
Other securities
SECURITIES AVAILABLE FOR SALE
Amortized Cost	8	7
Gross Unrealized Gains	4	4
Gross Unrealized Losses	0	0
Fair Value	12	11
HELD-TO-MATURITY SECURITIES
Amortized Cost	15	15
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	15	15
Mortgage-backed securities \| Agency commercial mortgage-backed securities
SECURITIES AVAILABLE FOR SALE
Amortized Cost	6,301	6,898
Gross Unrealized Gains	426	139
Gross Unrealized Losses	0	40
Fair Value	6,727	6,997
HELD-TO-MATURITY SECURITIES
Amortized Cost	3,805	3,940
Gross Unrealized Gains	278	78
Gross Unrealized Losses	0	9
Fair Value	4,083	$ 4,009
Securities available for sale
HELD-TO-MATURITY SECURITIES
Accrued interest	39
Securities held-to-maturity
HELD-TO-MATURITY SECURITIES
Accrued interest	$ 18

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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