Debt - Summary of Financial Covenants (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Debt Disclosure [Abstract]
Minimum fixed charge coverage ratio, actual	2.40%
Maximum total leverage ratio, actual	2.46%
Minimum liquidity, actual	$ 1,472
Minimum fixed charge coverage ratio, requirement	1.50%
Maximum total leverage ratio, requirement	4.25%
Minimum liquidity, requirement	$ 200