Retirement and Post-retirement Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension Benefit
Net Periodic Benefit Costs:
Service cost	$ 2	$ 2	$ 4	$ 4
Interest cost	4	4	8	8
Expected return on plan assets	(6)	(6)	(12)	(12)
Recognized actuarial loss	2	3	4	6
Settlement loss		2		2
Total	2	5	4	8
Post-retirement Benefit
Net Periodic Benefit Costs:
Service cost	5	5	10	10
Interest cost	10	10	20	20
Recognized actuarial loss	4	6	8	11
Total	19	21	38	41
Defined benefit plans
Net Periodic Benefit Costs:
Employer contributions	$ 1	$ 1	$ 2	$ 2