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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

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- Definition The amount of goodwill arising from a business combination that is expected to be deductible for tax purposes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479 + Details
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