Investment Securities - Schedule of Investment Securities Maturity Information (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Investment securities available for sale
Non-amortizing securities maturing in one year or less, cost	$ 9	$ 0
Non-amortizing securities maturing in after one through five years, cost	2,055	2,049
Non-amortizing securities maturing in after five through 10 years, cost	515	523
Non-amortizing securities maturing in after 10 years, cost	17	17
Investment securities available for sale, cost	9,726	9,215
Non-amortizing securities maturing in one year or less, fair value	9	0
Non-amortizing securities maturing in after one through five years, fair value	1,972	2,048
Non-amortizing securities maturing in after five through 10 years, fair value	520	548
Non-amortizing securities maturing in after 10 years, fair value	16	17
Investment securities available for sale, fair value	9,295	9,203
Investment securities held to maturity
Non-amortizing securities maturing in one year or less, cost	4	2
Non-amortizing securities maturing in after one through five years, cost	873	0
Non-amortizing securities maturing in after five through 10 years, cost	1,433	0
Investment securities held to maturity, cost	10,074	3,809
Non-amortizing securities maturing in one year or less, fair value	4	2
Non-amortizing securities maturing in after one through five years, fair value	836	0
Non-amortizing securities maturing in after five through 10 years, fair value	1,351	0
Investment securities held to maturity, cost, fair value	9,457	3,759
Government agency
Investment securities available for sale
Without single maturity date, cost	206	221
Investment securities available for sale, cost	206	221
Without single maturity date, fair value	206	221
Investment securities available for sale, fair value	206	221
Investment securities held to maturity
Investment securities held to maturity, cost	1,541
Investment securities held to maturity, cost, fair value	1,463
Residential mortgage-backed securities
Investment securities available for sale
Without single maturity date, cost	5,340	4,757
Investment securities available for sale, cost	5,340	4,757
Without single maturity date, fair value	5,052	4,729
Investment securities available for sale, fair value	5,052	4,729
Investment securities held to maturity
Without single maturity date, cost	4,776	2,322
Investment securities held to maturity, cost	4,776	2,322
Without single maturity date, fair value	4,461	2,306
Investment securities held to maturity, cost, fair value	4,461	2,306
Commercial mortgage-backed securities
Investment securities available for sale
Without single maturity date, cost	1,584	1,648
Investment securities available for sale, cost	1,584	1,648
Without single maturity date, fair value	1,520	1,640
Investment securities available for sale, fair value	1,520	1,640
Investment securities held to maturity
Without single maturity date, cost	2,988	1,485
Investment securities held to maturity, cost	2,988	1,485
Without single maturity date, fair value	2,805	1,451
Investment securities held to maturity, cost, fair value	$ 2,805	$ 1,451