Financial Instruments - Effect of Interest Rate Swaps on Results of Operations (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Interest expense	$ 1,690	$ 1,707	$ 1,665
Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain Recognized in OCI on Derivatives, Net of Tax	7
Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest expense	$ 20