Investments (Summary of Amount of Gross Unrealized Losses for Debt Securities and Estimated Fair Value) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Gross unrealized losses
Total investment securities, less than 12 months	$ 74	$ 73
Total investment securities, 12 months or more	1,447	1,386
Total investment securities, total	1,521	1,459
Estimated fair value
Total investment securities, less than 12 months	408	550
Total investment securities, 12 months or more	9,170	9,373
Total investment securities, total	9,578	9,923
Municipal securities
Gross unrealized losses
Available-for-sale, less than 12 Months	1	2
Available-for-sale, 12 Months or more	76	65
Available-for-sale, total	77	67
Estimated fair value
Available-for-sale, less than 12 Months	83	229
Available-for-sale, 12 months or more	1,154	1,061
Available-for-sale, total	1,237	1,290
U.S. Treasury securities
Gross unrealized losses
Available-for-sale, less than 12 Months	0	0
Available-for-sale, 12 Months or more	103	93
Available-for-sale, total	103	93
Estimated fair value
Available-for-sale, less than 12 Months	10	0
Available-for-sale, 12 months or more	298	308
Available-for-sale, total	308	308
Agency securities
Gross unrealized losses
Available-for-sale, less than 12 Months	0	0
Available-for-sale, 12 Months or more	33	33
Available-for-sale, total	33	33
Estimated fair value
Available-for-sale, less than 12 Months	0	5
Available-for-sale, 12 months or more	579	605
Available-for-sale, total	579	610
Agency guaranteed mortgage-backed securities
Gross unrealized losses
Available-for-sale, less than 12 Months	73	71
Available-for-sale, 12 Months or more	1,209	1,168
Available-for-sale, total	1,282	1,239
Estimated fair value
Available-for-sale, less than 12 Months	312	312
Available-for-sale, 12 months or more	6,665	6,902
Available-for-sale, total	6,977	7,214
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	25	25
Available-for-sale, total	25	25
Estimated fair value
Available-for-sale, less than 12 Months	3	4
Available-for-sale, 12 months or more	460	484
Available-for-sale, total	463	488
Other
Gross unrealized losses
Available-for-sale, less than 12 Months	0	0
Available-for-sale, 12 Months or more	1	2
Available-for-sale, total	1	2
Estimated fair value
Available-for-sale, less than 12 Months	0	0
Available-for-sale, 12 months or more	14	13
Available-for-sale, total	$ 14	$ 13

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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