Unaudited Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Current Assets
Cash and cash equivalents	$ 735	$ 967
Allowance for doubtful accounts - trade receivables	5	6
Trade receivables - third party and affiliates	792	706
Accumulated depreciation	2,164	2,039
Property, plant and equipment (net of accumulated depreciation - 2016: $2,164; 2015: $2,039; variable interest entity restricted - 2016: $754; 2015: $772)	3,588	3,609
Other assets	293	300
Finite-Lived Intangible Assets, Accumulated Amortization	538	528
Intangible assets (net of accumulated amortization - 2016: $538; 2015: $528; variable interest entity restricted - 2016: $26; 2015: $27)	$ 121	$ 125
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	22,737,630	19,916,490
Series A common stock, $0.0001 par value, 400,000,000 shares authorized (2016: 167,474,301 issued and 144,736,671 outstanding; 2015: 166,698,787 issued and 146,782,297 outstanding)
Stockholders' Equity
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	167,474,301	166,698,787
Common stock, shares outstanding	144,736,671	146,782,297
Series B common stock, $0.0001 par value, 100,000,000 shares authorized (2016 and 2015: 0 issued and outstanding)
Stockholders' Equity
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	0	0
Common stock, shares outstanding	0	0
Variable Interest Entity, Primary Beneficiary [Member]
Current Assets
Cash and cash equivalents	$ 23	$ 7
Trade receivables - third party and affiliates	5	6
Property, plant and equipment (net of accumulated depreciation - 2016: $2,164; 2015: $2,039; variable interest entity restricted - 2016: $754; 2015: $772)	754	772
Other assets	10	13
Intangible assets (net of accumulated amortization - 2016: $538; 2015: $528; variable interest entity restricted - 2016: $26; 2015: $27)	$ 26	$ 27