Securities - Available for Sale Securities (Unrealized Loss Position) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Held-to-maturity securities:
Temporarily impaired securities, fair value, less than 12 months	$ 19,329	$ 4,830
Temporarily impaired securities, gross unrealized losses, less than 12 months	414	58
Temporarily impaired securities, fair value, 12 months or longer	104	29
Temporarily impaired securities, gross unrealized losses, 12 months or longer	2	0
Temporarily impaired securities, fair value	19,433	4,859
Temporarily impaired securities, gross unrealized losses	416	58
U.S. Treasury, agencies and corporations
Securities available for sale:
Fair value, less than 12 months	4,886
Gross unrealized losses, less than 12 months	14
Fair value, 12 months or longer	0
Gross unrealized losses, 12 months or longer	0
Fair value	4,886
Gross unrealized losses	14
Agency residential collateralized mortgage obligations
Securities available for sale:
Fair value, less than 12 months	6,366	2,110
Gross unrealized losses, less than 12 months	207	25
Fair value, 12 months or longer	97	0
Gross unrealized losses, 12 months or longer	2	0
Fair value	6,463	2,110
Gross unrealized losses	209	25
Held-to-maturity securities:
Fair value, less than 12 months		0
Gross unrealized losses, less than 12 months		0
Fair value, 12 months or longer		24
Gross unrealized losses, 12 months or longer		0
Fair value		24
Gross unrealized losses		0
Agency residential collateralized mortgage obligations \| Maximum
Securities available for sale:
Gross unrealized losses, 12 months or longer		1
Agency commercial mortgage-backed securities
Securities available for sale:
Fair value, less than 12 months	5,421	2,709
Gross unrealized losses, less than 12 months	165	33
Fair value, 12 months or longer	0	0
Gross unrealized losses, 12 months or longer	0	0
Fair value	5,421	2,709
Gross unrealized losses	165	33
Asset-backed securities
Held-to-maturity securities:
Fair value, less than 12 months	9
Gross unrealized losses, less than 12 months	0
Fair value, 12 months or longer	1
Gross unrealized losses, 12 months or longer	0
Fair value	10
Gross unrealized losses	0
Asset-backed securities \| Maximum
Held-to-maturity securities:
Gross unrealized losses	1
Other securities
Held-to-maturity securities:
Fair value, less than 12 months	3	5
Gross unrealized losses, less than 12 months	0	0
Fair value, 12 months or longer	0	0
Gross unrealized losses, 12 months or longer	0	0
Fair value	3	5
Gross unrealized losses	0	0
Other securities \| Maximum
Held-to-maturity securities:
Gross unrealized losses, less than 12 months		1
Mortgage-backed securities \| Agency residential mortgage-backed securities
Securities available for sale:
Fair value, less than 12 months	2,644	6
Gross unrealized losses, less than 12 months	28	0
Fair value, 12 months or longer	6	5
Gross unrealized losses, 12 months or longer	0	0
Fair value	2,650	11
Gross unrealized losses	$ 28	0
Mortgage-backed securities \| Agency residential mortgage-backed securities \| Maximum
Securities available for sale:
Gross unrealized losses, less than 12 months		1
Gross unrealized losses, 12 months or longer		$ 1

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