Income (Loss) and Dividends per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)	6	5
Net income	$ (46)	$ 174
Weighted average common shares outstanding (in shares)	794	819
Effect of dilutive securities (in shares)	0	1
Weighted average common shares, diluted (in shares)	794	820
Net income (loss) per share:
Basic	$ (0.06)	$ 0.21
Per diluted share:
Diluted	(0.06)	0.21
Dividends per share (in dollars per share)	$ 0.05	$ 0.05