Financial Instruments - Carrying and Estimated Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Carrying And Estimated Fair Value [Line Items]
Long-term debt (including current maturities)	$ 1,304	$ 1,358
Net Carrying Amount
Carrying And Estimated Fair Value [Line Items]
Long-term debt (including current maturities)	1,308	1,361
Net Carrying Amount \| Equity swap agreement and foreign currency forward contracts
Equity swap agreement and foreign currency forward contracts:
Asset derivative contracts	5	4
Fair Value
Carrying And Estimated Fair Value [Line Items]
Long-term debt (including current maturities)	1,252	1,398
Fair Value \| Equity swap agreement and foreign currency forward contracts
Equity swap agreement and foreign currency forward contracts:
Asset derivative contracts	$ 5	$ 4

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

Reference 1: 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(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: 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(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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