CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ 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
Statement of Comprehensive Income [Abstract]
Net loss	$ (1,857)		$ (609)	$ 80	$ (593)		$ (880)	$ (1,547)	$ (2,386)		$ (3,020)
Change in value of pension and other postretirement liabilities:
Settlement adjustment	1	[1]	3		1	[1]			4	[1]	1	[1]
Comprehensive income (loss)	$ (1,856)		$ (606)	$ 80	$ (592)		$ (880)	$ (1,547)	$ (2,382)		$ (3,019)

[1] Tax benefits for the three months ended September 30, 2021 and 2020 were immaterial. Net of $1 million in taxes for the nine months ended September 30, 2021 and 2020, respectively.