Retirement and Postretirement Benefit Plans - Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Benefit
Net Periodic Benefit Costs
Service cost	$ 1	$ 2
Interest cost	4	4
Expected return on plan assets	(5)	(6)
Recognized actuarial loss	2	1
Recognized prior service cost	0	0
Total	2	1
Postretirement Benefit
Net Periodic Benefit Costs
Service cost	6	6
Interest cost	8	9
Expected return on plan assets	0	0
Recognized actuarial loss	2	4
Recognized prior service cost	(2)	0
Total	14	19
Defined benefit plans
Net Periodic Benefit Costs
Employer contributions	$ 1	$ 1