Securities - Fair Value of Debt Securities Available for Sale by Contractual Maturity (Details) $ in Millions	Sep. 30, 2019 USD ($)
Securities available for sale
One Year or Less	$ 100
Over One Year Through Five Years	1,973
Over Five Years Through Ten Years	6,033
Over Ten Years	9,145
Total Fair Value	17,251
U.S. Treasury and government agencies
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	1,240
Over Five Years Through Ten Years	3,200
Over Ten Years	35
Total Fair Value	4,475
U.S. government agency and government-sponsored agencies - residential mortgage-backed securities
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	241
Over Five Years Through Ten Years	1,087
Over Ten Years	5,346
Total Fair Value	6,674
Residential - non-agency
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	852
Total Fair Value	852
Commercial - non-agency
Securities available for sale
One Year or Less	32
Over One Year Through Five Years	0
Over Five Years Through Ten Years	789
Over Ten Years	1,750
Total Fair Value	2,571
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	463
Over Ten Years	1,061
Total Fair Value	1,524
Direct bank purchase bonds
Securities available for sale
One Year or Less	65
Over One Year Through Five Years	289
Over Five Years Through Ten Years	494
Over Ten Years	101
Total Fair Value	949
Other
Securities available for sale
One Year or Less	3
Over One Year Through Five Years	203
Over Five Years Through Ten Years	0
Over Ten Years	0
Total Fair Value	$ 206