Fair Value Disclosures - Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Commitments to extend, originate or purchase credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/Contract Amount	$ 72,435	$ 67,860
Fair Value	140	259
Residential mortgage loans sold with recourse
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/Contract Amount	419	490
Fair Value	3	5
CRE mortgages serviced for others covered by recourse provisions
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/Contract Amount	4,699	4,153
Fair Value	6	5
Letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/Contract Amount	2,389	2,466
Fair Value	$ 18	$ 21