Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Basic EPS
Net income (loss)	$ 708	$ 117
Less: Net income allocated to participating securities	(3)
Net income, net of participating securities	$ 705	$ 117
Weighted average number of basic shares	765.6	764.4
Basic EPS (in dollars per share)	$ 0.92	$ 0.15
Diluted EPS
Net income, net of participating securities	$ 705	$ 117
Weighted average number of basic shares	765.6	764.4
Dilutive effect of potentially dilutive securities (in shares)	1.4	0.8
Total diluted weighted average common shares	767.0	765.2
Diluted EPS (in dollars per share)	$ 0.92	$ 0.15