Fair Value of Financial Instruments - Carrying Values and Fair Values of Non-Current Financial Assets and Liabilities (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior, mezzanine, and other loans	$ 121	$ 142
Other noncurrent liabilities	(2,198)	(2,610)
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior, mezzanine, and other loans	121	142
Total noncurrent financial assets	121	142
Senior Notes	(4,927)	(5,087)
Commercial paper	(3,079)	(2,371)
Other long-term debt	(207)	(217)
Other noncurrent liabilities	(165)	(178)
Total noncurrent financial liabilities	(8,378)	(7,853)
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior, mezzanine, and other loans	108	130
Total noncurrent financial assets	108	130
Senior Notes	(4,810)	(5,126)
Commercial paper	(3,079)	(2,371)
Other long-term debt	(205)	(221)
Other noncurrent liabilities	(165)	(178)
Total noncurrent financial liabilities	$ (8,259)	$ (7,896)