Commitments and Contingencies - Credit Extension Commitments Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Legally binding unfunded commitments syndicated	$ 10,900	$ 10,500
Carrying amount credit extension commitments syndicated	1,800	1,900
Notional amount of credit extension commitments under fair value option	4,600	4,000
Unfunded loan commitments
Other Commitments [Line Items]
Fair value carrying amount, liabilities	$ 91	$ 99