Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Current Assets
Allowance for doubtful accounts - trade receivables	$ 9	$ 10
Accumulated depreciation	2,957	2,803
Cash and cash equivalents (variable interest entity restricted - 2019: $57; 2018: $24)	463	439
Trade receivables - third party and affiliates (net of allowance for doubtful accounts - 2019: $9; 2018: $10; variable interest entity restricted - 2019: $6; 2018: $6)	850	1,017
Property, plant and equipment (net of accumulated depreciation - 2019: $2,957; 2018: $2,803; variable interest entity restricted - 2019: $622; 2018: $659)	3,713	3,719
Intangible assets, net (variable interest entity restricted - 2019: $22; 2018: $23)	312	310
Other assets (variable interest entity restricted - 2019: $9; 2018: $5)	$ 338	$ 290
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	49,417,265	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	168,973,172	168,418,954
Common stock, shares outstanding	119,555,207	128,095,849
Variable Interest Entity, Primary Beneficiary [Member]
Current Assets
Cash and cash equivalents (variable interest entity restricted - 2019: $57; 2018: $24)	$ 57	$ 24
Trade receivables - third party and affiliates (net of allowance for doubtful accounts - 2019: $9; 2018: $10; variable interest entity restricted - 2019: $6; 2018: $6)	6	6
Property, plant and equipment (net of accumulated depreciation - 2019: $2,957; 2018: $2,803; variable interest entity restricted - 2019: $622; 2018: $659)	622	659
Intangible assets, net (variable interest entity restricted - 2019: $22; 2018: $23)	22	23
Other assets (variable interest entity restricted - 2019: $9; 2018: $5)	$ 9	$ 5