Securities - Fair Value of Debt Securities AFS Contractual Maturity (Details) $ in Millions	Dec. 31, 2016 USD ($)
Securities available for sale
One Year or Less	$ 5
Over One Year Through Five Years	809
Over Five Years Through Ten Years	4,674
Over Ten Years	8,648
Total Fair Value	14,136
U.S. Treasury
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	345
Over Five Years Through Ten Years	2,160
Over Ten Years	0
Total Fair Value	2,505
U.S. government agency and government-sponsored agencies
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	11
Over Five Years Through Ten Years	324
Over Ten Years	6,360
Total Fair Value	6,695
Privately issued
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	326
Total Fair Value	327
Privately issued - commercial mortgage-backed securities
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	0
Over Five Years Through Ten Years	0
Over Ten Years	664
Total Fair Value	664
Collateralized loan obligations
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	0
Over Five Years Through Ten Years	1,369
Over Ten Years	849
Total Fair Value	2,218
Other
Securities available for sale
One Year or Less	1
Over One Year Through Five Years	1
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	1
Over One Year Through Five Years	358
Over Five Years Through Ten Years	3,858
Over Ten Years	8,199
Total Fair Value	12,416
Direct bank purchase bonds
Securities available for sale
One Year or Less	4
Over One Year Through Five Years	369
Over Five Years Through Ten Years	816
Over Ten Years	424
Total Fair Value	1,613
Other
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	82
Over Five Years Through Ten Years	0
Over Ten Years	25
Total Fair Value	$ 107