Earnings Per Share (Schedule of Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ 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]
Net income (loss)	$ (593)	$ (880)	$ (1,547)	$ 49	$ 138	$ 594	$ (3,020)	$ 781
Number of common shares:
Weighted average outstanding (in shares)	571,872,413			539,221,101			551,162,559	539,315,170
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)	0			187,706			0	400,120
Effect of issuance of non-vested performance units (in shares)	0			629,380			0	727,359
Weighted average and potential dilutive outstanding (in shares)	571,872,413			540,038,187			551,162,559	540,442,649
Earnings per common share
Basic (in dollars per share)	$ (1.04)			$ 0.09			$ (5.48)	$ 1.45
Diluted (in dollars per share)	$ (1.04)			$ 0.09			$ (5.48)	$ 1.44