CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ 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
Statement of Comprehensive Income [Abstract]
Net loss		$ (609)	$ 80	$ (880)	$ (1,547)	$ (529)	$ (2,427)
Change in value of pension and other postretirement liabilities:
Settlement adjustment	[1]	3		0		3	0
Comprehensive income (loss)		$ (606)	$ 80	$ (880)	$ (1,547)	$ (526)	$ (2,427)

[1] Net of $1 million tax benefits for the three and six months ended June 30, 2021 and for the six months ended June 30, 2020. Tax benefits for the three months ended June 30, 2020 were immaterial.