Benefit Obligations (Schedule of Other Postemployment Obligations) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Postemployment benefits	$ 8	$ 9

The carrying amount as of the balance sheet date of the obligations recognized for the various benefits provided to former or inactive employees, their beneficiaries, and covered dependents after employment but before retirement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 712
-SubTopic 10
-Section 25
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6410138&loc=d3e79691-111665

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 712
-SubTopic 10
-Section 25
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6410138&loc=d3e79708-111665

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.15)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.15)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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