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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Earnings (loss) available to common stockholders	$ (1,841)	$ 1,024	$ (5,172)	$ 2,368
Basic weighted-average shares outstanding (in shares)	291.0	255.3	273.5	261.0
Effect of employee stock awards and warrants (in shares)	0.0	1.1	0.0	1.0
Diluted weighted-average shares outstanding (in shares)	291.0	256.4	273.5	262.0
Earnings (loss) per share, basic (in dollars per share)	$ (6.33)	$ 4.01	$ (18.91)	$ 9.07
Earnings (loss) per share, diluted (in dollars per share)	$ (6.33)	$ 3.99	$ (18.91)	$ 9.04