Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2019	Jun. 30, 2018
Income Tax Contingency [Line Items]
Provisional charges recorded	$ 174		$ 174
Income tax (expense) benefit	(235)	$ 32	(289)	$ 33
Income (loss) before income tax (expense) benefit	169	(251)	310	(252)
Income tax related to non-cash write-down of assets and investments		$ 121		121
Gross income tax paid			89	$ 69
Tax Cuts and Jobs Act of 2017 [Member]
Income Tax Contingency [Line Items]
Deemed patriation tax charge	34		34
Deferred deferred tax charge due to re-measurement of U.S. deferred tax assets	$ (140)		$ (140)
Scenario, Forecast [Member]
Income Tax Contingency [Line Items]
U.S. statutory federal tax rate					21.00%	28.00%