Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2	$ 6	$ 9	$ 13
Interest cost	17	59	64	118
Expected return on plan assets	(24)	(71)	(94)	(143)
Recognized net actuarial loss	12	34	54	69
Amortization of prior service cost (benefit)	0	1	0	1
Settlements	64	2	64	4
Net periodic benefit cost	71	31	97	62
Discontinued operations	0	24	20	48
Net amount recognized in Statement of Consolidated Operations	71	7	77	14
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	2	2	4
Interest cost	1	7	7	14
Recognized net actuarial loss	0	1	2	2
Amortization of prior service cost (benefit)	(1)	(2)	(3)	(3)
Curtailments	0	0	0	(58)
Net periodic benefit cost	1	8	8	(41)
Discontinued operations	0	7	6	(29)
Net amount recognized in Statement of Consolidated Operations	$ 1	$ 1	$ 2	$ (12)