Unaudited Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Current Assets
Cash and cash equivalents	$ 497	$ 439
Allowance for doubtful accounts - trade receivables	9	10
Trade receivables - third party and affiliates	947	1,017
Nontrade Receivables, Current	335	301
Accumulated depreciation	2,848	2,803
Property, plant and equipment (net of accumulated depreciation - 2019: $2,848; 2018: $2,803; variable interest entity restricted - 2019: $631; 2018: $659)	3,585	3,719
Other assets	344	290
Intangible assets (variable interest entity restricted - 2019: $22; 2018: $23)	$ 314	$ 310
Stockholders' Equity
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Treasury stock, shares	47,614,760	40,323,105
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	168,948,063	168,418,954
Common stock, shares outstanding	121,333,303	128,095,849
Variable Interest Entity, Primary Beneficiary [Member]
Current Assets
Cash and cash equivalents	$ 46	$ 24
Trade receivables - third party and affiliates	7	6
Nontrade Receivables, Current	0	0
Property, plant and equipment (net of accumulated depreciation - 2019: $2,848; 2018: $2,803; variable interest entity restricted - 2019: $631; 2018: $659)	631	659
Other assets	2	5
Intangible assets (variable interest entity restricted - 2019: $22; 2018: $23)	$ 22	$ 23