Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Settlements	$ 3	$ 64	$ 6	$ 64
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	2	2	9
Interest cost	12	17	24	64
Expected return on plan assets	(23)	(24)	(46)	(94)
Recognized net actuarial loss	15	12	29	54
Settlements	3	64	6	64
Net periodic benefit cost	8	71	15	97
Discontinued operations	0	0	0	20
Net amount recognized in continuing operations in Statement of Consolidated Operations	8	71	15	77
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	1	2
Interest cost	2	1	3	7
Recognized net actuarial loss	0	0	0	2
Amortization of prior service benefit	(3)	(1)	(4)	(3)
Net periodic benefit cost	0	1	0	8
Discontinued operations	0	0	0	6
Net amount recognized in continuing operations in Statement of Consolidated Operations	$ 0	$ 1	$ 0	$ 2