Earnings Per Share (Schedule of Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net income (loss)	$ (1,547)	$ 594
Number of common shares:
Weighted average outstanding (in shares)	540,308,491	539,721,751
Issued upon assumed exercise of outstanding stock options (in shares)	0	0
Effect of issuance of non-vested restricted common stock (in shares)	0	665,435
Effect of issuance of non-vested performance units (in shares)	0	933,301
Weighted average and potential dilutive outstanding (in shares)	540,308,491	541,320,487
Earnings per common share
Basic (in dollars per share)	$ (2.86)	$ 1.10
Diluted (in dollars per share)	$ (2.86)	$ 1.10