Employment Benefit Plans Net Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 46	$ 42	$ 46
Interest cost	82	88	95
Expected return on plan assets	(157)	(149)	(142)
Amortization of prior service credits	(1)	0	(1)
Amortization of net loss	1	0	1
Settlements	(1)	0	(1)
Net (benefit) cost recognized	(30)	(19)	(2)
Retiree Health and Welfare Benefits [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	1	1	1
Interest cost	8	9	10
Amortization of prior service credits	(2)	(2)	(2)
Amortization of net loss	0	0	1
Net (benefit) cost recognized	$ 7	$ 8	$ 10