Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Basic EPS:
Net income (loss)	$ 169	$ 19	$ (1,250)	$ (2,399)	$ (2,067)	$ (2,241)	$ (1,061)	$ (6,707)
Basic weighted average common shares outstanding (in shares)	648,564			509,049			642,432	454,523
Basic EPS (in dollars per share)	$ 0.26			$ (4.71)			$ (1.65)	$ (14.76)
Diluted EPS:
Interest expense on 6.50% convertible senior notes	$ 14
Net income (loss) for purposes of computing diluted EPS	$ 183			$ (2,399)			$ (1,061)	$ (6,707)
Dilutive effect of stock awards (in shares)	10,850			0			0	0
Assumed conversion of 6.50% convertible senior notes (in shares)	61,728			0			0	0
Diluted weighted average common shares outstanding (in shares)	721,142			509,049			642,432	454,523
Diluted EPS (in dollars per share)	$ 0.25			$ (4.71)			$ (1.65)	$ (14.76)
6.50% convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0			61,728			61,728	21,933
Restricted stock unit awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	1,172			4,559			3,272	5,091
Warrant | PSP1 Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0			25			5,555	2,131
Warrant | Treasury Loan Warrant
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0			1			1,731	0
Warrant | PSP3 Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	4,350			0			1,472	0
Warrant | PSP2 Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities (in shares)	0			0			1,329	0