Securities - Available for Sale Securities (Unrealized Loss Position) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Held-to-maturity securities:
Temporarily impaired securities, fair value, less than 12 months	$ 18,025	$ 4,830
Temporarily impaired securities, gross unrealized losses, less than 12 months	675	58
Temporarily impaired securities, fair value, 12 months or longer	28	29
Temporarily impaired securities, gross unrealized losses, 12 months or longer	0	0
Temporarily impaired securities, fair value	18,053	4,859
Temporarily impaired securities, gross unrealized losses	675	58
U.S. Treasury, agencies and corporations
Securities available for sale:
Fair value, less than 12 months	4,488	0
Gross unrealized losses, less than 12 months	13	0
Fair value, 12 months or longer	0	0
Gross unrealized losses, 12 months or longer	0	0
Fair value	4,488	0
Gross unrealized losses	13	0
Agency residential collateralized mortgage obligations
Securities available for sale:
Fair value, less than 12 months	5,401	2,110
Gross unrealized losses, less than 12 months	219	25
Fair value, 12 months or longer	0	0
Gross unrealized losses, 12 months or longer	0	0
Fair value	5,401	2,110
Gross unrealized losses	219	25
Held-to-maturity securities:
Fair value, less than 12 months	0	0
Gross unrealized losses, less than 12 months	0	0
Fair value, 12 months or longer	20	24
Gross unrealized losses, 12 months or longer	0	0
Fair value	20	24
Gross unrealized losses	0	0
Agency commercial mortgage-backed securities
Securities available for sale:
Fair value, less than 12 months	5,194	2,709
Gross unrealized losses, less than 12 months	394	33
Fair value, 12 months or longer	0	0
Gross unrealized losses, 12 months or longer	0	0
Fair value	5,194	2,709
Gross unrealized losses	394	33
Asset-backed securities
Held-to-maturity securities:
Fair value, less than 12 months	9	0
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	9	0
Gross unrealized losses	0	0
Other securities
Securities available for sale:
Fair value, less than 12 months	0
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	1
Gross unrealized losses	0
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
Mortgage-backed securities \| Agency residential mortgage-backed securities
Securities available for sale:
Fair value, less than 12 months	2,930	6
Gross unrealized losses, less than 12 months	49	0
Fair value, 12 months or longer	7	5
Gross unrealized losses, 12 months or longer	0	0
Fair value	2,937	11
Gross unrealized losses	$ 49	$ 0

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