Earnings (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Earnings (loss) available to common stockholders									$ (7,069)	$ 3,009	$ 2,122
Basic weighted-average shares outstanding (in shares)									279.4	258.8	275.5
Effect of share-based awards (in shares)									0.0	1.1	1.2
Diluted weighted-average shares outstanding (in shares)									279.4	259.9	276.7
Earnings per share, basic (in dollars per share)	$ (6.39)	$ (6.33)	$ (5.79)	$ (6.86)	$ 2.54	$ 4.01	$ 4.03	$ 1.09	$ (25.30)	$ 11.63	$ 7.70
Earnings per share, diluted (in dollars per share)					$ 2.53	$ 3.99	$ 4.02	$ 1.09	$ (25.30)	$ 11.58	$ 7.67