Commitments and Guarantees - Contractual Amounts of Credit-Related Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Unfunded credit facilities	$ 27,782	$ 26,488
Indemnified securities financing	380,389	381,817
Stable value protection	26,313	26,653
Standby letters of credit	$ 3,006	$ 3,158