Securities - Available for Sale Securities (Unrealized Loss Position) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Held-to-maturity securities:
Temporarily impaired securities, fair value, less than 12 months	$ 847	$ 7,250
Temporarily impaired securities, gross unrealized losses, less than 12 months	0	60
Temporarily impaired securities, fair value, 12 months or longer	100	7,382
Temporarily impaired securities, gross unrealized losses, 12 months or longer	1	113
Temporarily impaired securities, fair value	947	14,632
Temporarily impaired securities, gross unrealized losses	1	173
Collateralized mortgage Obligations
Securities available for sale:
Fair value, less than 12 months	371	3,432
Gross unrealized losses, less than 12 months	1,000,000	20
Fair value, 12 months or longer	58	3,221
Gross unrealized losses, 12 months or longer	1	51
Fair value	429	6,653
Gross unrealized losses	1	71
Held-to-maturity securities:
Fair value, less than 12 months	0	1,626
Gross unrealized losses, less than 12 months		14
Fair value, 12 months or longer	37	2,289
Gross unrealized losses, 12 months or longer	1,000,000	35
Fair value	37	3,915
Gross unrealized losses	0	49
Agency commercial mortgage-backed securities
Securities available for sale:
Fair value, less than 12 months		1,541
Gross unrealized losses, less than 12 months		17
Fair value, 12 months or longer		1,213
Gross unrealized losses, 12 months or longer		23
Fair value		2,754
Gross unrealized losses		40
Held-to-maturity securities:
Fair value, less than 12 months		518
Gross unrealized losses, less than 12 months		9
Fair value, 12 months or longer		0
Gross unrealized losses, 12 months or longer		0
Fair value		518
Gross unrealized losses		9
Asset-backed securities
Held-to-maturity securities:
Fair value, less than 12 months	1	11
Gross unrealized losses, less than 12 months	1,000,000	1,000,000
Fair value, 12 months or longer	0	0
Gross unrealized losses, 12 months or longer		0
Fair value	1	11
Gross unrealized losses	0	0
Other securities
Held-to-maturity securities:
Fair value, less than 12 months	10	3
Gross unrealized losses, less than 12 months	1,000,000	1,000,000
Fair value, 12 months or longer	0	0
Gross unrealized losses, 12 months or longer		0
Fair value	10	3
Gross unrealized losses	0	0
U.S. Treasury, agencies and corporations
Securities available for sale:
Fair value, less than 12 months	455	30
Gross unrealized losses, less than 12 months	1,000,000	1,000,000
Fair value, 12 months or longer	0	30
Gross unrealized losses, 12 months or longer		1,000,000
Fair value	455	60
Gross unrealized losses	0	0
Held-to-maturity securities:
Gross unrealized losses	0
Mortgage-backed securities \| Agency residential mortgage-backed securities
Securities available for sale:
Fair value, less than 12 months	10	33
Gross unrealized losses, less than 12 months	1,000,000	1,000,000
Fair value, 12 months or longer	5	629
Gross unrealized losses, 12 months or longer	1,000,000	4
Fair value	15	662
Gross unrealized losses	$ 0	4
Held-to-maturity securities:
Fair value, less than 12 months		56
Gross unrealized losses, less than 12 months		1,000,000
Fair value, 12 months or longer		0
Gross unrealized losses, 12 months or longer		0
Fair value		56
Gross unrealized losses		$ 0

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