Computation of Basic/Diluted Earnings Per Common Share - Computation EPS (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Consolidated net income (loss)	$ 127	$ (23)	$ 733	$ 474
Less: Distributed earnings to unvested stock-based awards that participate in earnings	0	0	(4)	(5)
Less: Undistributed earnings allocated to unvested stock-based awards that participate in earnings	(2)	0	(6)	(7)
Numerator for basic and diluted earnings (loss) per common share — income (loss) available to common shareholders	$ 125	$ (23)	$ 723	$ 462
Denominator:
Denominator for basic earnings per common share - weighted-average common shares outstanding (in shares)	730	718	727	714
Employee stock options and awards (in shares)	9	0	9	11
Denominator for diluted earnings per common share - weighted-average common shares outstanding plus dilutive common shares under treasury stock method (in shares)	739	718	736	725
Basic earnings (loss) per common share (in dollars per share)	$ 0.17	$ (0.03)	$ 0.99	$ 0.65
Diluted earnings (loss) per common share (in dollars per share)	$ 0.17	$ (0.03)	$ 0.98	$ 0.64