Securities - Details of Securities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
SECURITIES AVAILABLE FOR SALE
Amortized Cost (a)	$ 20,126	$ 21,692
Gross Unrealized Gains	688	266
Gross Unrealized Losses	7	115
Fair Value	20,807	21,843
HELD-TO-MATURITY SECURITIES
Amortized Cost (a)	9,638	10,067
Gross Unrealized Gains	374	107
Gross Unrealized Losses	0	58
Fair Value	10,012	10,116
Accrued interest	241	244
US Treasury and Government [Member]
SECURITIES AVAILABLE FOR SALE
Amortized Cost (a)	340	334
Gross Unrealized Gains	1	0
Gross Unrealized Losses	0	0
Fair Value	341	334
US States and Political Subdivisions Debt Securities [Member]
SECURITIES AVAILABLE FOR SALE
Amortized Cost (a)	4	4
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	4	4
Collateralized Mortgage Obligations [Member]
SECURITIES AVAILABLE FOR SALE
Amortized Cost (a)	11,705	12,772
Gross Unrealized Gains	342	82
Gross Unrealized Losses	2	71
Fair Value	12,045	12,783
HELD-TO-MATURITY SECURITIES
Amortized Cost (a)	5,354	5,692
Gross Unrealized Gains	157	23
Gross Unrealized Losses	0	49
Fair Value	5,511	5,666
Residential Mortgage Backed Securities [Member]
SECURITIES AVAILABLE FOR SALE
Amortized Cost (a)	1,472	1,677
Gross Unrealized Gains	67	41
Gross Unrealized Losses	0	4
Fair Value	1,539	1,714
HELD-TO-MATURITY SECURITIES
Amortized Cost (a)	390	409
Gross Unrealized Gains	19	6
Gross Unrealized Losses	0	0
Fair Value	409	415
Asset-backed Securities [Member]
HELD-TO-MATURITY SECURITIES
Amortized Cost (a)	11	11
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	11	11
Other Securities [Member]
SECURITIES AVAILABLE FOR SALE
Amortized Cost (a)	8	7
Gross Unrealized Gains	1	4
Gross Unrealized Losses	0	0
Fair Value	9	11
HELD-TO-MATURITY SECURITIES
Amortized Cost (a)	15	15
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	15	15
Other Mortgage-Backed Securities [Member] \| Commercial Mortgage Backed Securities [Member]
SECURITIES AVAILABLE FOR SALE
Amortized Cost (a)	6,597	6,898
Gross Unrealized Gains	277	139
Gross Unrealized Losses	5	40
Fair Value	6,869	6,997
HELD-TO-MATURITY SECURITIES
Amortized Cost (a)	3,868	3,940
Gross Unrealized Gains	198	78
Gross Unrealized Losses	0	9
Fair Value	4,066	$ 4,009
Securities Available for Sale [Member]
HELD-TO-MATURITY SECURITIES
Accrued interest	42
Securities Held-to-maturity [Member]
HELD-TO-MATURITY SECURITIES
Accrued interest	$ 19

Financing Receivable, Accrued Interest, Before Allowance For Credit Loss

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