Securities - Summary of Securities in Unrealized Loss Position (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Held-to-maturity securities:
Temporarily impaired securities, fair value, less than 12 months	$ 647	$ 10,991
Temporarily impaired securities, gross unrealized losses, less than 12 months	2	125
Temporarily impaired securities, fair value, 12 months or longer	24,158	16,041
Temporarily impaired securities, gross unrealized losses, 12 months or longer	943	570
Temporarily impaired securities, fair value	24,805	27,032
Temporarily impaired securities, gross unrealized losses	945	695
Government and agency bonds - U.S. [Member]
Securities available for sale:
Fair value, less than 12 months	0	41
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	1
Fair value, 12 months or longer	147	116
Gross unrealized losses, 12 months or longer	3	2
Fair value	147	157
Gross unrealized losses	3	2
Collateralized Mortgage Obligations [Member]
Securities available for sale:
Fair value, less than 12 months	570	6,153
Gross unrealized losses, less than 12 months (less than $1 million for agency residential mortgage-backed securities and U.S. Treasury, Agencies and Corporations)	2	74
Fair value, 12 months or longer	10,945	7,270
Gross unrealized losses, 12 months or longer	371	261
Fair value	11,515	13,423
Gross unrealized losses	373	335
Held-to-maturity securities:
Fair value, less than 12 months	0	2,201
Gross unrealized losses, less than 12 months (less than $1 million for agency commercial mortgage-backed securities and other securities)	0	27
Fair value, 12 months or longer	6,416	5,599
Gross unrealized losses, 12 months or longer (less than $1 million for other securities in 2017)	254	197
Fair value	6,416	7,800
Gross unrealized losses (less than $1 million for other securities)	254	224
Commercial Mortgage Backed Securities [Member]
Securities available for sale:
Fair value, less than 12 months	0	205
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	4
Fair value, 12 months or longer	1,729	1,649
Gross unrealized losses, 12 months or longer	132	62
Fair value	1,729	1,854
Gross unrealized losses		66
Held-to-maturity securities:
Fair value, less than 12 months	73	1,470
Gross unrealized losses, less than 12 months (less than $1 million for agency commercial mortgage-backed securities and other securities)	1	12
Fair value, 12 months or longer	3,359	495
Gross unrealized losses, 12 months or longer (less than $1 million for other securities in 2017)	133	32
Fair value	3,432	1,965
Gross unrealized losses (less than $1 million for other securities)	133	44
Other Securities [Member]
Held-to-maturity securities:
Fair value, less than 12 months	0	3
Gross unrealized losses, less than 12 months (less than $1 million for agency commercial mortgage-backed securities and other securities)	0	1
Fair value, 12 months or longer	0	4
Gross unrealized losses, 12 months or longer (less than $1 million for other securities in 2017)	0	1
Fair value	0	7
Gross unrealized losses (less than $1 million for other securities)	0	0
Other Mortgage-Backed Securities [Member] \| Residential Mortgage Backed Securities [Member]
Securities available for sale:
Fair value, less than 12 months	4	666
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	7
Fair value, 12 months or longer	1,087	702
Gross unrealized losses, 12 months or longer	36	13
Fair value	1,091	1,368
Gross unrealized losses	36	20
Held-to-maturity securities:
Fair value, less than 12 months	0	252
Gross unrealized losses, less than 12 months (less than $1 million for agency commercial mortgage-backed securities and other securities)	0	1
Fair value, 12 months or longer	475	206
Gross unrealized losses, 12 months or longer (less than $1 million for other securities in 2017)	14	3
Fair value	475	458
Gross unrealized losses (less than $1 million for other securities)	14	$ 4
Other Mortgage-Backed Securities [Member] \| Commercial Mortgage Backed Securities [Member]
Securities available for sale:
Gross unrealized losses	$ 132

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