This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 25
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8813-108599

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_EquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Equity Method Investments - Schedule of Equity Method Investments (Details) - USD ($) $ in Millions	Sep. 30, 2018	Aug. 28, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Carrying Value	$ 671		$ 686
USG Boral Building Products
Schedule of Equity Method Investments [Line Items]
Carrying Value	$ 669		$ 679
Ownership Percentage	50.00%	50.00%	50.00%
Other equity method investments
Schedule of Equity Method Investments [Line Items]
Carrying Value	$ 2		$ 7
Other equity method investments \| Minimum
Schedule of Equity Method Investments [Line Items]
Ownership Percentage			33.00%
Other equity method investments \| Maximum
Schedule of Equity Method Investments [Line Items]
Ownership Percentage	50.00%		50.00%