Securities - Details of Securities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
SECURITIES AVAILABLE FOR SALE
Amortized Cost	$ 21,692	$ 19,917
Gross Unrealized Gains	266	55
Gross Unrealized Losses	115	544
Fair Value	21,843	19,428
HELD-TO-MATURITY SECURITIES
Amortized Cost	10,067	11,519
Gross Unrealized Gains	107	4
Gross Unrealized Losses	58	401
Fair Value	10,116	11,122
U.S. Treasury, Agencies, and Corporations [Member]
SECURITIES AVAILABLE FOR SALE
Amortized Cost	334	150
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	3
Fair Value	334	147
State and municpal bonds [Member]
SECURITIES AVAILABLE FOR SALE
Amortized Cost	4	7
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	4	7
Collateralized Mortgage Obligations [Member]
SECURITIES AVAILABLE FOR SALE
Amortized Cost	12,772	14,315
Gross Unrealized Gains	82	20
Gross Unrealized Losses	71	373
Fair Value	12,783	13,962
HELD-TO-MATURITY SECURITIES
Amortized Cost	5,692	7,021
Gross Unrealized Gains	23	2
Gross Unrealized Losses	49	254
Fair Value	5,666	6,769
Residential Mortgage Backed Securities [Member]
SECURITIES AVAILABLE FOR SALE
Amortized Cost	1,677	2,128
Gross Unrealized Gains	41	13
Gross Unrealized Losses	4	36
Fair Value	1,714	2,105
HELD-TO-MATURITY SECURITIES
Amortized Cost	409	490
Gross Unrealized Gains	6	0
Gross Unrealized Losses	0	14
Fair Value	415	476
Asset-backed Securities [Member]
HELD-TO-MATURITY SECURITIES
Amortized Cost	11	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	11	0
Other Securities [Member]
SECURITIES AVAILABLE FOR SALE
Amortized Cost	7	17
Gross Unrealized Gains	4	3
Gross Unrealized Losses	0	0
Fair Value	11	20
HELD-TO-MATURITY SECURITIES
Amortized Cost	15	12
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	15	12
Other Mortgage-Backed Securities [Member] \| Commercial Mortgage Backed Securities [Member]
SECURITIES AVAILABLE FOR SALE
Amortized Cost	6,898	3,300
Gross Unrealized Gains	139	19
Gross Unrealized Losses	40	132
Fair Value	6,997	3,187
HELD-TO-MATURITY SECURITIES
Amortized Cost	3,940	3,996
Gross Unrealized Gains	78	2
Gross Unrealized Losses	9	133
Fair Value	$ 4,009	$ 3,865

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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