Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Basic EPS:
Net income (loss)	$ (2,067)	$ (2,241)	$ 662	$ 185	$ (4,308)	$ 847
Weighted average common shares outstanding (in shares)	428,807		445,008		427,260	448,479
Basic EPS (in dollars per share)	$ (4.82)		$ 1.49		$ (10.08)	$ 1.89
Diluted EPS:
Net income (loss) for purposes of computing diluted EPS	$ (2,067)		$ 662		$ (4,308)	$ 847
Share computation for diluted EPS:
Basic weighted average common shares outstanding (in shares)	428,807		445,008		427,260	448,479
Dilutive effect of stock awards (in shares)	0		579		0	1,029
Diluted weighted average common shares outstanding (in shares)	428,807		445,587		427,260	449,508
Diluted EPS (in dollars per share)	$ (4.82)		$ 1.49		$ (10.08)	$ 1.88
Restricted stock unit awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	5,781		3,087		5,357	2,677
PSP Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	6,368		0		3,184	0
6.50% convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	4,070		0		2,035	0