Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator for earnings (loss) per share, basic
Income (loss) from continuing operations attributable to controlling interest									$ 778	$ 865	$ (1,839)
Undistributed earnings allocable to participating securities									(14)	(8)
Income (loss) from continuing operations available to shareholders									$ 764	$ 857	$ (1,839)
Denominator for earnings (loss) per share, basic
Weighted-average shares outstanding	371.0	365.0	365.0	364.0	364.0	364.0	363.0	363.0	367.0	363.0	362.0
Weighted-average shares for per share calculation, basic	371.0	365.0	365.0	364.0	364.0	364.0	363.0	363.0	367.0	363.0	362.0
Per share earnings (loss) from continuing operations, basic									$ 2.08	$ 2.36	$ (5.02)
Numerator for earnings (loss) per share, diluted
Income (loss) from continuing operations attributable to controlling interest									$ 778	$ 865	$ (1,839)
Undistributed earnings allocable to participating securities									(14)	(8)
Income (loss) from continuing operations available to shareholders									$ 764	$ 857	$ (1,839)
Denominator for earnings (loss) per share, diluted
Weighted-average shares outstanding	371.0	365.0	365.0	364.0	364.0	364.0	363.0	363.0	367.0	363.0	362.0
Weighted-average shares for per share calculation, diluted	371.0	365.0	365.0	364.0	364.0	364.0	363.0	363.0	367.0	363.0	362.0
Per share earnings (loss) from continuing operations, diluted									$ 2.08	$ 2.36	$ (5.02)
Share-based awards
Denominator for earnings (loss) per share, diluted
Share-based awards excluded from earnings per share calculation (in shares)									2.5	3.3	2.5