Defined Benefit Postretirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Amortization:
Net settlement loss	$ (7)	$ (2)	$ (7)	$ (7)
Estimated future contributions over the remainder of the current year	16		16
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	5	10	9
Interest cost	2	7	5	14
Expected return on plan assets	(2)	(8)	(5)	(16)
Amortization:
– prior service cost (credit)	(2)	(2)	(4)	(4)
– actuarial loss	2	2	5	4
Net settlement loss	14	2	16	2
Net curtailment gain	(3)	0	(3)	0
Net periodic benefit cost	16	6	24	9
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	0	1	1	2
Expected return on plan assets	0	0	0	0
Amortization:
– prior service cost (credit)	(5)	(4)	(9)	(8)
– actuarial loss	1	0	1	0
Net settlement loss	0	0	0	0
Net curtailment gain	(14)	0	(14)	0
Net periodic benefit cost	$ (18)	$ (3)	(21)	$ (6)
Payment for other postretirement benefits			8
Funded Plan
Amortization:
Payment for pension benefits			12
Unfunded Plan
Amortization:
Payment for pension benefits			$ 14