Securities - Securities by Maturity (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Amortized Cost of Securities Available for sale, Due in one year or less	$ 3,918
Amortized Cost of Securities Available for sale, Due after one through five years	14,490
Amortized Cost of Securities Available for sale, Due after five through ten years	4,340
Amortized Cost of Securities Available for sale, Due after ten years	2
Amortized Cost	22,750	$ 21,692
Fair Value of Securities Available for sale, Due in one year or less	3,928
Fair Value of Securities Available for sale, Due after one through five years	15,024
Fair Value of Securities Available for sale, Due after five through ten years	4,646
Fair Value of Securities Available for sale, Due after ten years	2
Total Fair Value of Securities Available For Sale	23,600	21,843
Amortized Cost of Held-to-Maturity Securities, Due in one year or less	126
Amortized Cost of Held-to-Maturity Securities, Due after one through five years	6,323
Amortized Cost of Held-to-Maturity Securities, Due after five through ten years	2,626
Amortized Cost of Held-to-Maturity Securities, Due after ten years	0
Amortized Cost	9,075	10,067
Fair Value of Held-to-Maturity Securities, Due in one year or less	128
Fair Value of Held-to-Maturity Securities, Due after one through five years	6,564
Fair Value of Held-to-Maturity Securities, Due after five through ten years	2,828
Fair Value of Held-to-Maturity Securities, Due after ten years	0
Total Fair Value of Held-to-Maturity Securities	$ 9,520	$ 10,116