Commitments and Contingencies - Credit Extension Commitments Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Legally binding unfunded commitments syndicated	$ 10,900	$ 10,700
Carrying amount credit extension commitments syndicated	826	813
Deferred revenue	17	16
Other liabilities reserve for unfunded lending commitments	809	797
Notional amount of credit extension commitments under fair value option	4,800	3,100
Unfunded loan commitments
Other Commitments [Line Items]
Fair value carrying amount, liabilities	$ 116	$ 169