Commitments and Contingencies - Credit Extension Commitments Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Legally binding unfunded commitments syndicated	$ 10,500	$ 10,600
Carrying amount credit extension commitments syndicated	1,900	829
Notional amount of credit extension commitments under fair value option	4,000	4,400
Unfunded loan commitments
Other Commitments [Line Items]
Fair value carrying amount, liabilities	$ 99	$ 90