Securities - Summary of Securities in Unrealized Loss Position (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Held-to-maturity securities:
Temporarily impaired securities, fair value, less than 12 months	$ 7,250	$ 647
Temporarily impaired securities, gross unrealized losses, less than 12 months	60	2
Temporarily impaired securities, fair value, 12 months or longer	7,382	24,158
Temporarily impaired securities, gross unrealized losses, 12 months or longer	113	943
Temporarily impaired securities, fair value	14,632	24,805
Temporarily impaired securities, gross unrealized losses	173	945
U.S. Treasury, Agencies, and Corporations [Member]
Securities available for sale:
Fair value, less than 12 months	30	0
Gross unrealized losses, less than 12 months (less than $1 million for agency residential mortgage-backed securities and U.S. Treasury, Agencies and Corporations)		0
Fair value, 12 months or longer	30	147
Gross unrealized losses, 12 months or longer	1	3
Fair value	60	147
Gross unrealized losses	0	3
Collateralized Mortgage Obligations [Member]
Securities available for sale:
Fair value, less than 12 months	3,432	570
Gross unrealized losses, less than 12 months (less than $1 million for agency residential mortgage-backed securities and U.S. Treasury, Agencies and Corporations)	20	2
Fair value, 12 months or longer	3,221	10,945
Gross unrealized losses, 12 months or longer	51	371
Fair value	6,653	11,515
Gross unrealized losses	71	373
Held-to-maturity securities:
Fair value, less than 12 months	1,626	0
Gross unrealized losses, less than 12 months (less than $1 million for agency commercial mortgage-backed securities and other securities)	14	0
Fair value, 12 months or longer	2,289	6,416
Gross unrealized losses, 12 months or longer (less than $1 million for other securities in 2017)	35	254
Fair value	3,915	6,416
Gross unrealized losses (less than $1 million for other securities)	49	254
Commercial Mortgage Backed Securities [Member]
Securities available for sale:
Fair value, less than 12 months	1,541	0
Gross unrealized losses, less than 12 months (less than $1 million for agency residential mortgage-backed securities and U.S. Treasury, Agencies and Corporations)	17	0
Fair value, 12 months or longer	1,213	1,729
Gross unrealized losses, 12 months or longer	23	132
Fair value	2,754	1,729
Gross unrealized losses		132
Held-to-maturity securities:
Fair value, less than 12 months	518	73
Gross unrealized losses, less than 12 months (less than $1 million for agency commercial mortgage-backed securities and other securities)	9	1
Fair value, 12 months or longer	0	3,359
Gross unrealized losses, 12 months or longer (less than $1 million for other securities in 2017)	0	133
Fair value	518	3,432
Gross unrealized losses (less than $1 million for other securities)	9	133
Asset-backed Securities [Member]
Held-to-maturity securities:
Fair value, less than 12 months	11
Gross unrealized losses, less than 12 months (less than $1 million for agency commercial mortgage-backed securities and other securities)	1
Fair value, 12 months or longer	0
Gross unrealized losses, 12 months or longer (less than $1 million for other securities in 2017)	0
Fair value	11
Gross unrealized losses (less than $1 million for other securities)	0
Other Securities [Member]
Held-to-maturity securities:
Fair value, less than 12 months	3
Gross unrealized losses, less than 12 months (less than $1 million for agency commercial mortgage-backed securities and other securities)	1
Fair value, 12 months or longer	0
Gross unrealized losses, 12 months or longer (less than $1 million for other securities in 2017)	0
Fair value	3
Gross unrealized losses (less than $1 million for other securities)	0
Other Mortgage-Backed Securities [Member] \| Residential Mortgage Backed Securities [Member]
Securities available for sale:
Fair value, less than 12 months	33	4
Gross unrealized losses, less than 12 months (less than $1 million for agency residential mortgage-backed securities and U.S. Treasury, Agencies and Corporations)	1	1
Fair value, 12 months or longer	629	1,087
Gross unrealized losses, 12 months or longer	4	36
Fair value	662	1,091
Gross unrealized losses	4	36
Held-to-maturity securities:
Fair value, less than 12 months	56	0
Gross unrealized losses, less than 12 months (less than $1 million for agency commercial mortgage-backed securities and other securities)	1	0
Fair value, 12 months or longer	0	475
Gross unrealized losses, 12 months or longer (less than $1 million for other securities in 2017)	0	14
Fair value	56	475
Gross unrealized losses (less than $1 million for other securities)	0	$ 14
Other Mortgage-Backed Securities [Member] \| Commercial Mortgage Backed Securities [Member]
Securities available for sale:
Gross unrealized losses	$ 40

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