Securities - Details of Securities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
SECURITIES AVAILABLE FOR SALE
Amortized Cost	$ 26,054	$ 21,692
Gross Unrealized Gains	854	266
Gross Unrealized Losses	13	115
Fair Value	26,895	21,843
HELD-TO-MATURITY SECURITIES
Amortized Cost	8,384	10,067
Gross Unrealized Gains	458	107
Gross Unrealized Losses	0	58
Fair Value	8,842	10,116
Accrued interest	235	244
U.S. Treasury, agencies and corporations
SECURITIES AVAILABLE FOR SALE
Amortized Cost	4,463	334
Gross Unrealized Gains	1	0
Gross Unrealized Losses	0	0
Fair Value	4,464	334
States and political subdivisions
SECURITIES AVAILABLE FOR SALE
Amortized Cost	3	4
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	3	4
Collateralized mortgage Obligations
SECURITIES AVAILABLE FOR SALE
Amortized Cost	13,403	12,772
Gross Unrealized Gains	336	82
Gross Unrealized Losses	7	71
Fair Value	13,732	12,783
HELD-TO-MATURITY SECURITIES
Amortized Cost	4,308	5,692
Gross Unrealized Gains	141	23
Gross Unrealized Losses	0	49
Fair Value	4,449	5,666
Agency residential mortgage-backed securities
SECURITIES AVAILABLE FOR SALE
Amortized Cost	1,256	1,677
Gross Unrealized Gains	71	41
Gross Unrealized Losses	1	4
Fair Value	1,326	1,714
HELD-TO-MATURITY SECURITIES
Amortized Cost	313	409
Gross Unrealized Gains	11	6
Gross Unrealized Losses	0	0
Fair Value	324	415
Asset-backed securities
HELD-TO-MATURITY SECURITIES
Amortized Cost	22	11
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	22	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	6,921	6,898
Gross Unrealized Gains	442	139
Gross Unrealized Losses	5	40
Fair Value	7,358	6,997
HELD-TO-MATURITY SECURITIES
Amortized Cost	3,726	3,940
Gross Unrealized Gains	306	78
Gross Unrealized Losses	0	9
Fair Value	4,032	$ 4,009
Securities available for sale
HELD-TO-MATURITY SECURITIES
Accrued interest	39
Securities held-to-maturity
HELD-TO-MATURITY SECURITIES
Accrued interest	$ 17

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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