Securities - Securities by Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Amortized Cost of Securities Available for sale, Due in one year or less	$ 490
Amortized Cost of Securities Available for sale, Due after one through five years	17,438
Amortized Cost of Securities Available for sale, Due after five through ten years	3,756
Amortized Cost of Securities Available for sale, Due after ten years	8
Amortized Cost	21,692	$ 19,917
Fair Value of Securities Available for sale, Due in one year or less	494
Fair Value of Securities Available for sale, Due after one through five years	17,486
Fair Value of Securities Available for sale, Due after five through ten years	3,856
Fair Value of Securities Available for sale, Due after ten years	7
Total Fair Value of Securities Available-for-sale	21,843	19,428
Amortized Cost of Held-to-Maturity Securities, Due in one year or less	66
Amortized Cost of Held-to-Maturity Securities, Due after one through five years	7,173
Amortized Cost of Held-to-Maturity Securities, Due after five through ten years	2,828
Amortized Cost of Held-to-Maturity Securities, Due after ten years	0
Amortized Cost	10,067	11,519
Fair Value of Held-to-Maturity Securities, Due in one year or less	66
Fair Value of Held-to-Maturity Securities, Due after one through five years	7,178
Fair Value of Held-to-Maturity Securities, Due after five through ten years	2,872
Fair Value of Held-to-Maturity Securities, Due after ten years	0
Total Fair Value of Held-to-Maturity Securities	$ 10,116	$ 11,122