Unaudited Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Current Assets
Cash and cash equivalents	$ 491	$ 439
Allowance for doubtful accounts - trade receivables	9	10
Trade receivables - third party and affiliates	971	1,017
Nontrade Receivables, Current	332	301
Accumulated depreciation	2,828	2,803
Property, plant and equipment (net of accumulated depreciation - 2019: $2,828; 2018: $2,803; variable interest entity restricted - 2019: $641; 2018: $659)	3,642	3,719
Other assets	320	290
Intangible assets (variable interest entity restricted - 2019: $23; 2018: $23)	$ 327	$ 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	45,170,482	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	168,910,831	168,418,954
Common stock, shares outstanding	123,740,349	128,095,849
Variable Interest Entity, Primary Beneficiary [Member]
Current Assets
Cash and cash equivalents	$ 23	$ 24
Trade receivables - third party and affiliates	5	6
Nontrade Receivables, Current	0	0
Property, plant and equipment (net of accumulated depreciation - 2019: $2,828; 2018: $2,803; variable interest entity restricted - 2019: $641; 2018: $659)	641	659
Other assets	3	5
Intangible assets (variable interest entity restricted - 2019: $23; 2018: $23)	$ 23	$ 23