Earnings (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic EPS:
Net income (loss)	$ (2,399)	$ (2,067)	$ (2,241)	$ 425	$ 662	$ 185	$ (6,707)	$ 1,272
Weighted average common shares outstanding (in shares)	509,049			441,915			454,523	446,291
Basic EPS (in dollars per share)	$ (4.71)			$ 0.96			$ (14.76)	$ 2.85
Diluted EPS:
Net income (loss) for purposes of computing diluted EPS	$ (2,399)			$ 425			$ (6,707)	$ 1,272
Share computation for diluted EPS:
Basic weighted average common shares outstanding (in shares)	509,049			441,915			454,523	446,291
Dilutive effect of stock awards (in shares)	0			486			0	848
Diluted weighted average common shares outstanding (in shares)	509,049			442,401			454,523	447,139
Diluted EPS (in dollars per share)	$ (4.71)			$ 0.96			$ (14.76)	$ 2.84
Restricted stock unit awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	4,559			2,590			5,091	2,648
PSP Warrants | Payroll Support Program Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	25			0			2,131	0
PSP Warrants | Treasury Loan Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	1			0			0	0
6.50% convertible senior notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities	61,728			0			21,933	0