Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Line Items]
Deferred income taxes		$ (14)	$ 192	$ (51)
Federal net operating loss carryforwards net of valuation allowances		23
Foreign net operating loss carryforwards		903
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities		3	0	$ 0
Deferred Tax Liabilities, Undistributed Foreign Earnings		699
Internal Revenue Service (IRS)
Income Tax Disclosure [Line Items]
Federal net operating loss carryforwards net of valuation allowances		4,900
Provision adjustment due to corporate tax rate change [Member]
Income Tax Disclosure [Line Items]
Deferred income taxes		$ (30)	317
Provision adjustment due to anticipated repatriation of foreign earnings [Member]
Income Tax Disclosure [Line Items]
Deferred income taxes	$ (30)		$ (104)