Investments (Summary of Amount of Gross Unrealized Losses for Debt Securities and Estimated Fair Value) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Gross unrealized losses
Total investment securities, less than 12 months	$ 127	$ 21
Total investment securities, 12 months or more	32	36
Total investment securities, total	159	57
Estimated fair value
Total investment securities, less than 12 months	6,952	1,625
Total investment securities, 12 months or more	1,000	1,261
Total investment securities, total	7,952	2,886
Municipal securities
Gross unrealized losses
Held-to-maturity, less than 12 Months	2	1
Available-for-sale, less than 12 Months	3	0
Held-to-maturity, 12 months or more	0	0
Available-for-sale, 12 Months or more	0	0
Held-to-maturity, total	2	1
Available-for-sale, total	3	0
Estimated fair value
Held-to-maturity, less than 12 Months	149	96
Available-for-sale, less than 12 Months	217	19
Held-to-maturity, 12 months or more	14	12
Available-for-sale, 12 months or more	0	0
Held-to-maturity, total	163	108
Available-for-sale, total	217	19
U.S. Treasury, agencies and corporations
Gross unrealized losses
Available-for-sale, less than 12 Months	27	13
Available-for-sale, 12 Months or more	0	0
Available-for-sale, total	27	13
Estimated fair value
Available-for-sale, less than 12 Months	128	142
Available-for-sale, 12 months or more	0	0
Available-for-sale, total	128	142
Agency securities
Gross unrealized losses
Available-for-sale, less than 12 Months	0	0
Available-for-sale, 12 Months or more	0	0
Available-for-sale, total	0	0
Estimated fair value
Available-for-sale, less than 12 Months	105	6
Available-for-sale, 12 months or more	1	2
Available-for-sale, total	106	8
Agency guaranteed mortgage-backed securities
Gross unrealized losses
Available-for-sale, less than 12 Months	95	7
Available-for-sale, 12 Months or more	1	1
Available-for-sale, total	96	8
Estimated fair value
Available-for-sale, less than 12 Months	6,353	1,197
Available-for-sale, 12 months or more	125	179
Available-for-sale, total	6,478	1,376
Small Business Administration loan-backed securities
Gross unrealized losses
Available-for-sale, less than 12 Months	0	0
Available-for-sale, 12 Months or more	31	35
Available-for-sale, total	31	35
Estimated fair value
Available-for-sale, less than 12 Months	0	15
Available-for-sale, 12 months or more	860	1,068
Available-for-sale, total	860	1,083
Other
Gross unrealized losses
Available-for-sale, less than 12 Months	0	0
Available-for-sale, 12 Months or more	0	0
Available-for-sale, total	0	0
Estimated fair value
Available-for-sale, less than 12 Months	0	150
Available-for-sale, 12 months or more	0	0
Available-for-sale, total	0	150
Available-for-sale
Gross unrealized losses
Available-for-sale, less than 12 Months	125	20
Available-for-sale, 12 Months or more	32	36
Available-for-sale, total	157	56
Estimated fair value
Available-for-sale, less than 12 Months	6,803	1,529
Available-for-sale, 12 months or more	986	1,249
Available-for-sale, total	$ 7,789	$ 2,778