Securities - Amortized Cost and Estimated Fair Value by Contractual Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
AFS, Amortized Cost
Due in one year or less	$ 285
Due after one year through five years	1,674
Due after five years through ten years	502
Due after ten years	24,101
Total debt securities	26,562	$ 25,689
AFS, Fair Value
Due in one year or less	285
Due after one year through five years	1,631
Due after five years through ten years	503
Due after ten years	23,896
Total debt securities	26,315	25,038
HTM, Amortized Cost
Due in one year or less	1
Due after one year through five years	3,300
Due after five years through ten years	597
Due after ten years	16,197
Total debt securities	20,095	20,552
HTM, Fair Value
Due in one year or less	1
Due after one year through five years	3,289
Due after five years through ten years	591
Due after ten years	16,005
Total debt securities	$ 19,886	$ 20,047