Commitments and Contingencies - Credit Extension Commitments Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Legally binding unfunded commitments syndicated	$ 10,800	$ 11,000
Carrying amount credit extension commitments syndicated	808	793
Deferred revenue	16	16
Other liabilities reserve for unfunded lending commitments	792	777
Notional amount of credit extension commitments under fair value option	3,200	4,800
Unfunded loan commitments
Other Commitments [Line Items]
Fair value carrying amount liabilities	$ 70	$ 120