Income (Loss) and Dividends per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)	5	8
Net income	$ 174	$ 356
Weighted average common shares outstanding (in shares)	819	851
Effect of dilutive securities (in shares)	1	1
Weighted average common shares, diluted (in shares)	820	852
Net income per share:
Basic	$ 0.21	$ 0.42
Per diluted share:
Diluted	0.21	0.42
Dividends per share (in dollars per share)	$ 0.05	$ 0.05