Employment 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 Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10	$ 12	$ 31	$ 35
Interest Cost	22	23	66	71
Expected return on plan assets	(37)	(35)	(111)	(107)
Net cost (credit) recognized	(5)	0	(14)	(1)
Retiree Health and Welfare Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost			1	1
Interest Cost	3	3	7	8
Amortization of prior service cost (credit)	(1)	(1)	(2)	(2)
Net cost (credit) recognized	$ 2	$ 2	$ 6	$ 7