Commitments and Contingencies - Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Unfunded Loan Commitment [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/Contract Amount	$ 177,598	$ 72,435
Residential mortgage loans sold with recourse
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/Contract Amount	371	419
CRE mortgages serviced for others covered by recourse provisions
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/Contract Amount	8,676	4,699
Letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional/Contract Amount	$ 5,181	$ 2,389