Securities - Carrying Amount and Fair Value Securities Held to Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Securities held to maturity
Over One Year Through Five Years, Carrying Amount	$ 538
Over Five Years Through Ten Years, Carrying Amount	1,118
Over Ten Years, Carrying Amount	8,502
Total securities held to maturity, carrying amount	10,158	$ 8,291
Over One Year Through Five Years, Fair Value	543
Over Five Years Through Ten Years, Fair Value	1,151
Over Ten Years, Fair Value	8,513
Total securities held to maturity, Fair Value	10,207	8,412
U.S. Treasury
Securities held to maturity
Over One Year Through Five Years, Carrying Amount	489
Over Five Years Through Ten Years, Carrying Amount	0
Over Ten Years, Carrying Amount	0
Total securities held to maturity, carrying amount	489	486
Over One Year Through Five Years, Fair Value	493
Over Five Years Through Ten Years, Fair Value	0
Over Ten Years, Fair Value	0
Total securities held to maturity, Fair Value	493	489
U.S. government sponsored agencies
Securities held to maturity
Over One Year Through Five Years, Carrying Amount	0
Over Five Years Through Ten Years, Carrying Amount	220
Over Ten Years, Carrying Amount	0
Total securities held to maturity, carrying amount	220	125
Over One Year Through Five Years, Fair Value	0
Over Five Years Through Ten Years, Fair Value	216
Over Ten Years, Fair Value	0
Total securities held to maturity, Fair Value	216	125
U.S. government agency and government-sponsored agencies - residential mortgage-backed securities
Securities held to maturity
Over One Year Through Five Years, Carrying Amount	0
Over Five Years Through Ten Years, Carrying Amount	99
Over Ten Years, Carrying Amount	7,683
Total securities held to maturity, carrying amount	7,782	5,942
Over One Year Through Five Years, Fair Value	0
Over Five Years Through Ten Years, Fair Value	100
Over Ten Years, Fair Value	7,690
Total securities held to maturity, Fair Value	7,790	6,013
Commercial Mortgage Backed Securities US Government Agencies and Government Sponsored Agencies [Member]
Securities held to maturity
Over One Year Through Five Years, Carrying Amount	49
Over Five Years Through Ten Years, Carrying Amount	799
Over Ten Years, Carrying Amount	819
Total securities held to maturity, carrying amount	1,667
Over One Year Through Five Years, Fair Value	50
Over Five Years Through Ten Years, Fair Value	835
Over Ten Years, Fair Value	823
Total securities held to maturity, Fair Value	1,708
U.S. government agency and government-sponsored agencies - commercial mortgage-backed securities
Securities held to maturity
Total securities held to maturity, carrying amount	1,667	1,738
Total securities held to maturity, Fair Value	$ 1,708	$ 1,785

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
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-Name Accounting Standards Codification
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Fair value of held-to-maturity debt securities maturing in the sixth fiscal year through the tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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