Investment Securities (Gross Unrealized Loss and Fair Value of Securities Available for Sale Without an Allowance for Credit Losses) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	$ (274)	$ (42)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	42,958	5,185
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(16)	(27)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	1,758	1,724
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(290)	(69)
Debt securities, available-for-sale, unrealized loss position	44,716	6,909
U.S. Treasury and government agencies
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(146)	(13)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	17,168	603
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(146)	(13)
Debt securities, available-for-sale, unrealized loss position	17,168	603
Residential mortgage-backed | Mortgage-backed Securities Agency
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(122)	(8)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	24,527	3,152
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(3)	(2)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	442	82
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(125)	(10)
Debt securities, available-for-sale, unrealized loss position	24,969	3,234
Residential mortgage-backed | Mortgage-backed Securities Non-agency
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss		(7)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value		119
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(5)	(7)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	155	73
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(5)	(14)
Debt securities, available-for-sale, unrealized loss position	155	192
Commercial mortgage-backed | Mortgage-backed Securities Agency
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(2)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	274
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(1)	(2)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	65	149
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(3)	(2)
Debt securities, available-for-sale, unrealized loss position	339	149
Commercial mortgage-backed | Mortgage-backed Securities Non-agency
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss		(13)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value		972
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(4)	(7)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	710	714
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(4)	(20)
Debt securities, available-for-sale, unrealized loss position	710	1,686
Asset-backed
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(3)	(1)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	793	339
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	(3)	(9)
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer - fair value	386	706
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(6)	(10)
Debt securities, available-for-sale, unrealized loss position	1,179	$ 1,045
Other
Debt Securities, Available-for-sale [Line Items]
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months, accumulated loss	(1)
Debt securities, available-for-sale, continuous unrealized loss position, less than 12 months - fair value	196
Debt securities, available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss
Debt securities, available-for-sale, unrealized loss position, accumulated loss	(1)
Debt securities, available-for-sale, unrealized loss position	$ 196