Securities - Fair Value of Debt Securities AFS Contractual Maturity (Details) $ in Millions	Dec. 31, 2018 USD ($)
Securities available for sale
One Year or Less	$ 30
Over One Year Through Five Years	2,112
Over Five Years Through Ten Years	4,458
Over Ten Years	9,714
Total Fair Value	16,314
U.S. Treasury
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	1,284
Over Five Years Through Ten Years	2,145
Over Ten Years	0
Total Fair Value	3,429
U.S. government agency and government-sponsored agencies
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	212
Over Five Years Through Ten Years	1,306
Over Ten Years	6,489
Total Fair Value	8,007
Privately issued
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	864
Total Fair Value	864
Privately issued - commercial mortgage-backed securities
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	25
Over Five Years Through Ten Years	43
Over Ten Years	1,094
Total Fair Value	1,162
Collateralized loan obligations
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	1
Over Five Years Through Ten Years	352
Over Ten Years	1,121
Total Fair Value	1,474
Other
Securities available for sale
One Year or Less	1
Over One Year Through Five Years	3
Over Five Years Through Ten Years	0
Over Ten Years	0
Total Fair Value	4
Asset Liability Management securities
Securities available for sale
One Year or Less	1
Over One Year Through Five Years	1,525
Over Five Years Through Ten Years	3,846
Over Ten Years	9,568
Total Fair Value	14,940
Direct bank purchase bonds
Securities available for sale
One Year or Less	26
Over One Year Through Five Years	424
Over Five Years Through Ten Years	612
Over Ten Years	128
Total Fair Value	1,190
Other
Securities available for sale
One Year or Less	3
Over One Year Through Five Years	163
Over Five Years Through Ten Years	0
Over Ten Years	18
Total Fair Value	$ 184