Earnings Per Share (Schedule of Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended					6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018		Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income	$ 138	$ 594	$ 51	[1]	$ 208	$ 732	$ 259	[1]
Participating securities - mandatory convertible preferred stock	0		0			0	2
Net Income Attributable to Common Stock	$ 138		$ 51			$ 732	$ 257
Number of common shares:
Weighted average outstanding (in shares)	539,005,941		581,159,200			539,362,984	576,255,744
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)	311,732		480,580			481,948	683,562
Effect of issuance of non-vested performance units (in shares)	629,380		1,238,326			779,810	1,283,434
Weighted average and potential dilutive outstanding (in shares)	539,947,053		582,878,106			540,624,742	578,222,740
Earnings per common share
Basic (in dollars per share)	$ 0.26		$ 0.09			$ 1.36	$ 0.45
Diluted (in dollars per share)	$ 0.26		$ 0.09			$ 1.35	$ 0.44

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