Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2018
Income Tax Contingency [Line Items]
Income tax expense	$ 55,000,000	$ 235,000,000	$ 105,000,000	$ 289,000,000
Income (loss) before income tax (expense) benefit	$ 174,000,000	169,000,000	352,000,000	310,000,000
Provisional charges recorded		$ 174,000,000		174,000,000
Gross income tax paid			75,000,000	89,000,000
Income tax refunds			$ 10,000,000	$ 0
U.S. Tax Cuts and Jobs Act [Member]
Income Tax Contingency [Line Items]
Income tax expense					$ 237,000,000
US Statutory Federal Tax Rate [Member]
Income Tax Contingency [Line Items]
U.S. statutory federal tax rate					21.00%