Retirement and Post-retirement Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Benefit
Net Periodic Benefit Costs:
Service cost	$ 2	$ 2	$ 6	$ 6
Interest cost	4	4	12	12
Expected return on plan assets	(6)	(6)	(18)	(18)
Recognized actuarial loss	2	3	6	9
Settlement loss				2
Total	2	3	6	11
Post-retirement Benefit
Net Periodic Benefit Costs:
Service cost	5	4	15	14
Interest cost	9	9	29	29
Recognized actuarial loss	3	3	11	14
Total	17	16	55	57
Defined benefit plans
Net Periodic Benefit Costs:
Employer contributions	$ 1	$ 0	$ 3	$ 2