Commitments and Guarantees - Contractual Amounts of Credit-Related Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Unfunded credit facilities	$ 29,951	$ 28,951
Indemnified securities financing	387,314	342,337
Standby letters of credit	$ 2,973	$ 2,985
Unfunded commitments to extend credit, short term	75.00%
Term of unfunded commitment		1 year