Securities - Carrying Amount and Fair Value of Securities Held to Maturity by Contractual Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Securities held to maturity
Within One Year, Carrying Amount	$ 444
Within One Year, Fair Value	444
Over One Year Through Five Years, Carrying Amount	1,280
Over One Year Through Five Years, Fair Value	1,295
Over Five Years Through Ten Years, Carrying Amount	1,295
Over Five Years Through Ten Years, Fair Value	1,286
Over Ten Years, Carrying Amount	7,390
Over Ten Years, Fair Value	7,306
Total securities held to maturity, carrying amount	10,409	$ 10,901
Securities held to maturity	10,331	10,720
U.S. Treasury
Securities held to maturity
Within One Year, Carrying Amount	423
Within One Year, Fair Value	423
Over One Year Through Five Years, Carrying Amount	4
Over One Year Through Five Years, Fair Value	4
Over Five Years Through Ten Years, Carrying Amount	0
Over Five Years Through Ten Years, Fair Value	0
Over Ten Years, Carrying Amount	0
Over Ten Years, Fair Value	0
Total securities held to maturity, carrying amount	427	528
Securities held to maturity	427	527
US Government Agencies Debt Securities [Member]
Securities held to maturity
Within One Year, Carrying Amount	0
Within One Year, Fair Value	0
Over One Year Through Five Years, Carrying Amount	500
Over One Year Through Five Years, Fair Value	500
Over Five Years Through Ten Years, Carrying Amount	350
Over Five Years Through Ten Years, Fair Value	350
Over Ten Years, Carrying Amount	0
Over Ten Years, Fair Value	0
Total securities held to maturity, carrying amount	850	722
Securities held to maturity	850	723
U.S. government agency and government-sponsored agencies - residential mortgage-backed securities
Securities held to maturity
Within One Year, Carrying Amount	0
Within One Year, Fair Value	0
Over One Year Through Five Years, Carrying Amount	0
Over One Year Through Five Years, Fair Value	0
Over Five Years Through Ten Years, Carrying Amount	945
Over Five Years Through Ten Years, Fair Value	936
Over Ten Years, Carrying Amount	6,804
Over Ten Years, Fair Value	6,730
Total securities held to maturity, carrying amount	7,749	8,207
Securities held to maturity	7,666	$ 8,027
U.S. government agency and government-sponsored agencies - commercial mortgage-backed securities
Securities held to maturity
Within One Year, Carrying Amount	21
Within One Year, Fair Value	21
Over One Year Through Five Years, Carrying Amount	776
Over One Year Through Five Years, Fair Value	791
Over Five Years Through Ten Years, Carrying Amount	0
Over Five Years Through Ten Years, Fair Value	0
Over Ten Years, Carrying Amount	586
Over Ten Years, Fair Value	576
Total securities held to maturity, carrying amount	1,383
Securities held to maturity	$ 1,388

Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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