Retirement and Postretirement Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Benefit
Net Periodic Benefit Costs
Service cost	$ 1	$ 2	$ 2	$ 4
Interest cost	3	4	7	8
Expected return on plan assets	(5)	(6)	(10)	(12)
Recognized actuarial loss	3	1	5	2
Recognized prior service cost	0	0	0	0
Total	2	1	4	2
Postretirement Benefit
Net Periodic Benefit Costs
Service cost	5	6	11	12
Interest cost	10	9	18	18
Expected return on plan assets	0	0	0	0
Recognized actuarial loss	2	6	4	10
Recognized prior service cost	(2)	0	(4)	0
Total	15	21	29	40
Defined benefit plans
Net Periodic Benefit Costs
Employer contributions	$ 0	$ 1	$ 1	$ 2