Other Assets - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Other Assets [Abstract]
Accumulated depreciation and amortization	$ 8,160	$ 7,770
Property, leasehold improvements and equipment used for operation	$ 6,040	$ 5,930
Amortization period - Capitalized costs of software developed or obtained for internal use	3 years