Income (Loss) and Dividends per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)	7		6		7	6
Net income	$ (750)	$ (46)	$ 161	$ 174	$ (796)	$ 335
Weighted average common shares outstanding (in shares)	790		813		793	817
Effect of dilutive securities (in shares)	0		1		0	0
Weighted average common shares, diluted (in shares)	790		814		793	817
Net income (loss) per share:
Basic (in dollars per share)	$ (0.95)		$ 0.20		$ (1.00)	$ 0.41
Per diluted share:
Diluted (in dollars per share)	(0.95)		0.20		(1.00)	0.41
Dividends per share (in dollars per share)	$ 0	$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.10