Supplemental Information ( Additional Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Accrued Liabilities [Abstract]
Accrued liabilities	$ 675		$ 675		$ 657
Accrued Rebates, Current	112		112		108
Due to Affiliate, Current	45		45		$ 37
Increase (Decrease) in Capital Expenditure Accrual			(8)	$ 8
One-time settlement gain		$ 2	23	6
Income (Loss) from Subsidiaries, Net of Tax	5	4	17	11
Interest Income, Other	4	$ 1	13	$ 2
2021 Notes [Member]
Accrued Liabilities [Abstract]
Gain on debt redemption			$ 6
Other Income [Member]
Accrued Liabilities [Abstract]
Defined Benefit Plan, Net Periodic Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income	$ 16