Commitments and Guarantees - Contractual Amounts of Credit-Related Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Unfunded credit facilities	$ 26,488	$ 26,993
Indemnified securities financing	381,817	360,452
Stable value protection	26,653	27,182
Standby letters of credit	$ 3,158	$ 3,459