Commitments and Contingencies - Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Residential Mortgage
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional amount	$ 328	$ 371	$ 419
CRE
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional amount	9,019	8,676
Commitments to extend, originate or purchase credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional amount	186,731	177,598
Letters of credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Notional amount	$ 5,066	$ 5,181