Employment Benefit Plans Net Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 42	$ 46	$ 48
Interest cost	88	95	90
Expected return on plan assets	(149)	(142)	(138)
Amortization of prior service credits	0	(1)	(1)
Amortization of net loss	0	1	2
Settlements	0	(1)	(1)
Net (benefit) cost recognized	(19)	(2)	0
Retiree Health and Welfare Benefits [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	1	1	1
Interest cost	9	10	10
Amortization of prior service credits	(2)	(2)	(2)
Amortization of net loss	0	1	2
Net (benefit) cost recognized	$ 8	$ 10	$ 11