Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Basic EPS:
Net income (loss)	$ 19	$ (1,250)	$ (2,067)	$ (2,241)	$ (1,231)	$ (4,308)
Basic (in shares)	644,123		428,807		639,366	427,260
Basic EPS (in dollars per share)	$ 0.03		$ (4.82)		$ (1.92)	$ (10.08)
Diluted EPS:
Net income (loss) for purposes of computing diluted EPS	$ 19		$ (2,067)		$ (1,231)	$ (4,308)
Dilutive effect of stock awards (in shares)	12,249		0		0	0
Diluted (in shares)	656,372		428,807		639,366	427,260
Diluted EPS (in dollars per share)	$ 0.03		$ (4.82)		$ (1.92)	$ (10.08)
6.50% convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	61,728		4,070		61,728	2,035
Restricted stock unit awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	1,182		5,781		3,191	5,357
Warrant | PSP1 Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	0		6,368		5,632	3,184
Warrant | Treasury Loan Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	0		0		1,755	0
Warrant | PSP2 Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	0		0		1,242	0
Warrant | PSP3 Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	0		0		34	0