Income Taxes - Valuation Allowances Rollforward (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance at January 1	$ (1,755)	$ (1,403)	$ (864)
Valuation Allowance [Line Items]
Balance at December 31	(3,024)	(1,755)	(1,403)
U.S. Foreign Tax Credits [Member]
Valuation Allowance [Line Items]
Change in valuation allowances	(1,287)	(477)	(384)
Foreign and State Net Operating Loss Carryforwards [Member]
Valuation Allowance [Line Items]
Change in valuation allowances	75	13	10
Foreign Capitalized Costs [Member]
Valuation Allowance [Line Items]
Change in valuation allowances	$ (57)	$ 112	$ (165)