Acquisitions - Summary of Purchase Price Allocation (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2015
Minimum [Member]
Business Acquisition [Line Items]
Estimated useful lives		1 year
Maximum [Member]
Business Acquisition [Line Items]
Estimated useful lives		20 years
2016 Acquisition [Member]
Business Acquisition [Line Items]
Goodwill	$ 116
2016 Acquisition [Member] | Trade Names [Member]
Business Acquisition [Line Items]
Estimated useful lives	20 years
2016 Acquisition [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Estimated useful lives	10 years
Series of Individually Immaterial Business Acquisitions [Member] | Trade Names [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated useful lives			1 year
Series of Individually Immaterial Business Acquisitions [Member] | Trade Names [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated useful lives			20 years
Series of Individually Immaterial Business Acquisitions [Member] | Customer Relationships [Member] | Minimum [Member]
Business Acquisition [Line Items]
Estimated useful lives			6 years
Series of Individually Immaterial Business Acquisitions [Member] | Customer Relationships [Member] | Maximum [Member]
Business Acquisition [Line Items]
Estimated useful lives			10 years