Earnings Per Share (Schedule of Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended							9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018		Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income	$ 49	$ 138	$ 594	$ (29)	[1]	$ 51	$ 208	$ 781	$ 230	[1]
Participating securities – mandatory convertible preferred stock	0			0				0	1
Net Income (Loss) Attributable to Common Stock	$ 49			$ (29)				$ 781	$ 229
Number of common shares:
Weighted average outstanding (in shares)	539,221,101			581,171,753				539,315,170	577,912,421
Issued upon assumed exercise of outstanding stock options (in shares)	0			0				0	0
Effect of issuance of non-vested restricted common stock (in shares)	187,706			0				400,120	640,365
Effect of issuance of non-vested performance units (in shares)	629,380			0				727,359	1,276,072
Weighted average and potential dilutive outstanding (in shares)	540,038,187			581,171,753				540,442,649	579,828,858
Earnings per common share
Basic (in dollars per share)	$ 0.09			$ (0.05)				$ 1.45	$ 0.40
Diluted (in dollars per share)	$ 0.09			$ (0.05)				$ 1.44	$ 0.39

[1] In 2018, deferred tax activity incurred in other comprehensive income was offset by a valuation allowance.