Securities - Carrying Amount and Fair Value Securities Held to Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Securities held to maturity
Over One Year Through Five Years, Carrying Amount	$ 704
Over Five Years Through Ten Years, Carrying Amount	2,235
Over Ten Years, Carrying Amount	6,473
Total securities held to maturity, carrying amount	9,421	$ 10,901
Over One Year Through Five Years, Fair Value	724
Over Five Years Through Ten Years, Fair Value	2,234
Over Ten Years, Fair Value	6,541
Total securities held to maturity, Fair Value	9,508	10,720
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost	9
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value	9
US Treasury and Government [Member]
Securities held to maturity
Over One Year Through Five Years, Carrying Amount	0
Over Five Years Through Ten Years, Carrying Amount	1,350
Over Ten Years, Carrying Amount	0
Total securities held to maturity, carrying amount	1,359	1,250
Over One Year Through Five Years, Fair Value	0
Over Five Years Through Ten Years, Fair Value	1,344
Over Ten Years, Fair Value	0
Total securities held to maturity, Fair Value	1,353	1,250
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost	9
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value	9
U.S. government agency and government-sponsored agencies - residential mortgage-backed securities
Securities held to maturity
Over One Year Through Five Years, Carrying Amount	704
Over Five Years Through Ten Years, Carrying Amount	885
Over Ten Years, Carrying Amount	6,473
Total securities held to maturity, carrying amount	8,062	9,651
Over One Year Through Five Years, Fair Value	724
Over Five Years Through Ten Years, Fair Value	890
Over Ten Years, Fair Value	6,541
Total securities held to maturity, Fair Value	8,155	$ 9,470
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost	0
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value	$ 0

Amount of investment in debt security measured at amortized cost (held-to-maturity).

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