Employee Benefit Plans - Individually Significant Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Multiemployer Plans [Line Items]
High end of funded percentage of multiemployer plans in critical status		65.00%
High end of funded percentage of multiemployer plans in endangered status		80.00%
Surcharge percentage during first twelve months on contribution rates for plans certified as endangered, seriously endangered or critical		5.00%
Period for which surcharge is 5% on contribution rates for plans certified as endangered, seriously endangered or critical		12 months
Accrued benefit liabilities		$ 29	$ 37
Surcharge percentage after first twelve months on contribution rates for plans certified as endangered, seriously endangered or critical		10.00%
Minimum percentage of total contributions provided by the Company relating to multiemployer plans		5.00%
Company Contributions		$ 47	47	$ 43
Minimum [Member]
Multiemployer Plans [Line Items]
Projected insolvency period		15 years
Maximum [Member]
Multiemployer Plans [Line Items]
Projected insolvency period		20 years
Western Pennsylvania Teamsters and Employers Pension Plan [Member]
Multiemployer Plans [Line Items]
Company Contributions		$ 1	1	1
Multiemployer Health and Welfare Plan [Member]
Multiemployer Plans [Line Items]
Company Contributions		42	$ 40	33
Withdrawal from Multiemployer Pension Plans [Member]
Multiemployer Plans [Line Items]
Charge to "Operating" expenses	$ 11	12		$ 51
Withdrawal from Multiemployer Pension Plans [Member] | Western Pennsylvania Teamsters and Employers Pension Plan [Member]
Multiemployer Plans [Line Items]
Charge to "Operating" expenses		$ 11