Environmental Matters (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($) DisposalSite	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Environmental Remediation Obligations [Abstract]
Number of disposal sites \| DisposalSite	19
Environmental expenses	$ 12	$ 10	$ 9
Environmental liabilities	10	9
Asset retirement obligation	$ 26	$ 26

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

Name:	us-gaap_AssetRetirementObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant