Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Settlements	$ 3	$ 3	$ 9	$ 67
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	3	10
Interest cost	12	17	36	81
Expected return on plan assets	(23)	(21)	(69)	(115)
Recognized net actuarial loss	14	12	43	66
Settlements	3	8	9	72
Net periodic (benefit) cost	7	17	22	114
Discontinued operations	0	0	0	20
Net amount recognized in continuing operations in Statement of Consolidated Operations	7	17	22	94
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	1	1	3
Interest cost	1	2	4	9
Recognized net actuarial loss	1	0	1	2
Amortization of prior service benefit	(3)	(2)	(7)	(5)
Curtailments	0	(2)	0	(2)
Net periodic (benefit) cost	(1)	(1)	(1)	7
Discontinued operations	0	0	0	6
Net amount recognized in continuing operations in Statement of Consolidated Operations	$ (1)	$ (1)	$ (1)	$ 1