Defined Benefit Postretirement Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Amortization:
Net settlement loss	$ 0	$ (5)
Estimated future contributions over the remainder of the current year	22
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	4
Interest cost	3	7
Expected return on plan assets	(3)	(8)
Amortization:
– prior service credit	(2)	(2)
– actuarial loss	3	2
Net settlement loss	2
Net periodic benefit cost	8	3
Payment for other postretirement benefit plans	20
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	1	1
Expected return on plan assets	0	0
Amortization:
– prior service credit	(4)	(4)
– actuarial loss	0	0
Net settlement loss	0	0
Net periodic benefit cost	(3)	$ (3)
Payment for other postretirement benefits	4
Funded Plan
Amortization:
Payment for pension benefits	6
Unfunded Plan
Amortization:
Payment for pension benefits	$ 5