Earnings (Loss) Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Earnings (loss) available to common stockholders	$ (1,627)	$ 1,052	$ (3,331)	$ 1,344
Basic weighted-average shares outstanding (in shares)	280.7	260.8	264.6	263.9
Effect of employee stock awards and warrants (in shares)	0.0	0.8	0.0	1.0
Diluted weighted-average shares outstanding (in shares)	280.7	261.6	264.6	264.9
Earnings (loss) per share, basic (in dollars per share)	$ (5.79)	$ 4.03	$ (12.59)	$ 5.09
Earnings (loss) per share, diluted (in dollars per share)	$ (5.79)	$ 4.02	$ (12.59)	$ 5.07