Commitments, Guarantees and Risks - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments And Contingencies Disclosure [Abstract]
Operating lease expiration minimum period	3 years
Operating lease expiration maximum period	5 years
Operating lease rental expense based on straight-line basis	$ 284	$ 268	$ 254
Termination fees	$ 67
Expiration period of termination fee	3 years