Financial Instruments - Effect of Interest Rate Swaps on Results of Operations (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Interest expense	$ 411	$ 427	$ 830	$ 843
Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Loss Recognized in OCI on Derivatives, Net of Tax			5
Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest expense			$ 13