Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2019
Income Tax Contingency [Line Items]
Income tax benefit related to release of valuation allowance	$ 33
Income tax expense	$ 5	$ 50
U.S. federal corporate statutory tax rate	21.00%
Reasonably possible decrease in gross unrecognized tax benefits from ongoing audits and settlement	$ 1
Foreign Tax Authority
Income Tax Contingency [Line Items]
Release of valuation allowance			$ 33