Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Basic EPS Calculation
Earnings available to common stockholders - Basic	$ (5,543)	$ 2,924	$ 14,824
Weighted-average number of common shares outstanding (in shares)	1,870	1,882	1,897
Add: Deferred awards held as stock units (in shares)	0	0	1
Total weighted-average number of common shares outstanding (in shares)	1,870	1,882	1,898
Earnings per share of common stock - Basic (in dollars per share)	$ (2.96)	$ 1.55	$ 7.81
Diluted EPS Calculation
Earnings available to common stockholders - Diluted	$ (5,543)	$ 2,924	$ 14,824
Weighted-average number of common shares outstanding (in shares)	1,870	1,882	1,897
Add: Deferred awards held as stock units (in shares)	0	0	1
Add: Dilutive effect of employee stock-based awards (in shares)	0	13	16
Total weighted-average number of common shares outstanding (in shares)	1,870	1,895	1,914
Earnings per share of common stock - Diluted (in dollars per share)	$ (2.96)	$ 1.54	$ 7.74
Antidilutive securities excluded from computation of earnings per share (in shares)	1