Fair Value Disclosures - Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Commitments to extend, originate or purchase credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/Contract Amount	$ 75,677	$ 72,435
Fair Value	262	280
Residential mortgage loans sold with recourse
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/Contract Amount	387	419
Fair Value	3	3
CRE mortgages serviced for others covered by recourse provisions
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/Contract Amount	4,691	4,699
Fair Value	6	6
Letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/Contract Amount	2,269	2,389
Fair Value	$ 16	$ 18