Significant Accounting Policies - Investments in Unconcolidated Joint Ventures (Details) $ in Millions	Dec. 31, 2017 USD ($)
USG Boral Building Products
Schedule of Equity Method Investments [Line Items]
Contingent consideration amount (up to)	$ 50

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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