Special Charges (Credits) - Components of Special Charges (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Other Income and Expenses [Abstract]
CARES Act grant	$ (1,132)	$ (1,494)	$ (4,021)	$ (3,083)
Impairment of assets	46	38	105	168
Severance and benefit costs	5	350	433	413
(Gains) losses on sale of assets and other special charges	(17)	25	60	35
Total operating special charges (credits)	(1,098)	(1,081)	(3,423)	(2,467)
Nonoperating unrealized (gains) losses on investments, net	34	(15)	(91)	295
Nonoperating debt extinguishment and modification fees	(12)	0	50	0
Nonoperating special termination benefits and settlement losses	0	415	46	646
Nonoperating credit loss on BRW Term Loan and related guarantee	0		0	697
Total nonoperating special charges and unrealized (gains) losses on investments, net	22	400	5	1,638
Total operating and nonoperating special charges (credits) and unrealized (gains) losses on investments, net	(1,076)	(681)	(3,418)	(829)
Income tax expense, net of valuation allowance	274	148	768	375
Total operating and nonoperating special charges (credits) and unrealized (gains) losses on investments, net of income taxes	$ (802)	$ (533)	$ (2,650)	$ (454)