Commitments and Guarantees - Contractual Amounts of Credit-Related Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Unfunded credit facilities	$ 26,654	$ 26,488
Indemnified securities financing	396,801	381,817
Stable value protection	26,252	26,653
Standby letters of credit	$ 2,955	$ 3,158