Income per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share [Abstract]
Income (loss) from continuing operations	$ 480	$ 1,096	$ (830)
Loss from discontinued operations	0	0	(4,893)
Net income (loss)	$ 480	$ 1,096	$ (5,723)
Weighted average common shares outstanding, basic	810	846	850
Weighted Average Number Diluted Shares Outstanding Adjustment	0	1	0
Weighted average common shares outstanding, diluted	810	847	850
Basic:
Income from continuing operations (in dollars per basic share)	$ 0.59	$ 1.30	$ (0.97)
Discontinued operations (in dollars per basic share)	0	0	(5.76)
Net income (in dollars per basic share)	0.59	1.30	(6.73)
Diluted:
Income from continuing operations (in dollars per diluted share)	0.59	1.29	(0.97)
Discontinued operations (in dollars per diluted share)	0	0	(5.76)
Net income (in dollars per diluted share)	$ 0.59	$ 1.29	$ (6.73)
Antidilutive securities excluded from computation of earnings per share	6	6	11
Common Stock, Dividends, Per Share, Cash Paid	$ 0.20	$ 0.20	$ 0.20