Securities - Fair Value of Debt Securities AFS Contractual Maturity (Details) $ in Millions	Dec. 31, 2015 USD ($)
Securities available for sale
One Year or Less	$ 73
Over One Year Through Five Years	394
Over Five Years Through Ten Years	3,492
Over Ten Years	10,377
Total Fair Value	14,336
US Treasury Securities
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	0
Over Five Years Through Ten Years	594
Over Ten Years	0
Total Fair Value	594
Residential mortgage-backed securities, U.S. government agency and government-sponsored agencies
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	19
Over Five Years Through Ten Years	388
Over Ten Years	6,794
Total Fair Value	7,201
Residential mortgage-backed securities, Privately issued
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	3
Over Five Years Through Ten Years	0
Over Ten Years	148
Total Fair Value	151
Commercial Mortgage Backed Securities Private Issue [Member]
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	0
Over Five Years Through Ten Years	36
Over Ten Years	1,510
Total Fair Value	1,546
Collateralized loan obligations
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	16
Over Five Years Through Ten Years	1,804
Over Ten Years	1,413
Total Fair Value	3,233
Other Asset Liability Management Securities, Other
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	2
Over Five Years Through Ten Years	5
Over Ten Years	0
Total Fair Value	7
Asset Liability Management securities
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	40
Over Five Years Through Ten Years	2,827
Over Ten Years	9,865
Total Fair Value	12,732
Other debt securities, Direct bank purchase bonds
Securities available for sale
One Year or Less	73
Over One Year Through Five Years	353
Over Five Years Through Ten Years	665
Over Ten Years	481
Total Fair Value	1,572
Other debt securities, Other
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	1
Over Five Years Through Ten Years	0
Over Ten Years	31
Total Fair Value	$ 32