Income (loss) and Dividends per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share (in shares)	6			6			6	5
Net income (loss)	$ (317)	$ (750)	$ (46)	$ 165	$ 161	$ 174	$ (1,113)	$ 500
Weighted average common shares outstanding (in shares)	790			802			792	813
Effect of dilutive securities (in shares)	0			1			0	0
Weighted average common shares, diluted (in shares)	790			803			792	813
Net income (loss) per share:
Basic (in dollars per share)	$ (0.40)			$ 0.21			$ (1.41)	$ 0.62
Per diluted share:
Diluted (in dollars per share)	(0.40)			0.21			(1.41)	0.62
Dividends per share (in dollars per share)	$ 0		$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.15