Unaudited Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Current Assets
Cash and cash equivalents	$ 952	$ 780
Allowance for doubtful accounts - trade receivables	6	9
Accumulated depreciation	1,990	1,816
Property, plant and equipment	3,778	3,733
Other assets	350	377
Finite-Lived Intangible Assets, Accumulated Amortization	$ 537	$ 556
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	19,916,490	13,266,625
Series A common stock, $0.0001 par value, 400,000,000 shares authorized (2015: 166,620,081 issued and 146,703,591 outstanding; 2014: 166,169,335 issued and 152,902,710 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	166,620,081	166,169,335
Common stock, shares outstanding	146,703,591	152,902,710
Series B common stock, $0.0001 par value, 100,000,000 shares authorized (2015 and 2014: 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	$ 1	$ 1
Property, plant and equipment	754	535
Other assets	$ 40	$ 24