Defined Benefit Postretirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Amortization:
Net settlement loss	$ (2)	$ 0	$ (7)	$ 3
Estimated future contributions over the remainder of the current year	12		12
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	5	9	9
Interest cost	7	6	14	13
Expected return on plan assets	(8)	(8)	(16)	(17)
Amortization:
– prior service credit	(2)	(3)	(4)	(5)
– actuarial loss	2	3	4	6
Net settlement loss	2	2	2	6
Net periodic benefit cost	6	5	9	12
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	1
Interest cost	1	2	2	4
Expected return on plan assets	0	0	0	0
Amortization:
– prior service credit	(4)	(2)	(8)	(4)
– actuarial loss	0	1	0	1
Net settlement loss	0	0	0	0
Net periodic benefit cost	$ (3)	$ 1	(6)	$ 2
Payment for other postretirement benefit plans			11
Funded Plan
Amortization:
Payment for pension benefits			29
Unfunded Plan
Amortization:
Payment for pension benefits			$ 3