Securities - Securities by Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Amortized Cost of Securities Available for sale, Due in one year or less	$ 275
Amortized Cost of Securities Available for sale, Due after one through five years	17,642
Amortized Cost of Securities Available for sale, Due after five through ten years	24,290
Amortized Cost of Securities Available for sale, Due after ten years	4,350
Amortized Cost	46,557
Fair Value of Securities Available for sale, Due in one year or less	277
Fair Value of Securities Available for sale, Due after one through five years	16,993
Fair Value of Securities Available for sale, Due after five through ten years	22,448
Fair Value of Securities Available for sale, Due after ten years	3,963
Fair Value	43,681	$ 45,364
Amortized Cost of Held-to-Maturity Securities, Due in one year or less	39
Amortized Cost of Held-to-Maturity Securities, Due after one through five years	4,861
Amortized Cost of Held-to-Maturity Securities, Due after five through ten years	1,971
Amortized Cost of Held-to-Maturity Securities, Due after ten years	0
Amortized Cost	6,871	7,539
Fair Value of Held-to-Maturity Securities, Due in one year or less	40
Fair Value of Held-to-Maturity Securities, Due after one through five years	4,717
Fair Value of Held-to-Maturity Securities, Due after five through ten years	1,930
Fair Value of Held-to-Maturity Securities, Due after ten years	0
Total Fair Value of Held-to-Maturity Securities	$ 6,687	$ 7,665