Securities - Fair Value of Debt Securities Available for Sale by Contractual Maturity (Details) $ in Millions	Mar. 31, 2020 USD ($)
Securities available for sale
One Year or Less	$ 123
Over One Year Through Five Years	701
Over Five Years Through Ten Years	6,650
Over Ten Years	7,666
Total Fair Value	15,140
U.S. Treasury and government agencies
Securities available for sale
One Year or Less	0
Over One Year Through Five Years	158
Over Five Years Through Ten Years	3,355
Over Ten Years	38
Total Fair Value	3,551
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	83
Over Five Years Through Ten Years	1,007
Over Ten Years	3,688
Total Fair Value	4,778
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	701
Total Fair Value	701
Commercial - non-agency
Securities available for sale
One Year or Less	28
Over One Year Through Five Years	0
Over Five Years Through Ten Years	1,443
Over Ten Years	2,192
Total Fair Value	3,663
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	376
Over Ten Years	952
Total Fair Value	1,328
Direct bank purchase bonds
Securities available for sale
One Year or Less	85
Over One Year Through Five Years	291
Over Five Years Through Ten Years	469
Over Ten Years	95
Total Fair Value	940
Other
Securities available for sale
One Year or Less	10
Over One Year Through Five Years	169
Over Five Years Through Ten Years	0
Over Ten Years	0
Total Fair Value	$ 179