Employment Benefit Plans Change in Benefit Obligation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of period	$ 2,387	$ 2,247
Service cost	46	42	$ 46
Interest cost	82	88	95
Actuarial loss (gain)	(158)	166
Benefits Paid	(149)	(144)
Settlements	(10)	(12)
Projected benefit obligation at end of period	2,198	2,387	2,247
Component representing future salary increases	(136)	(135)
Accumulated benefit obligation at end of period	2,062	2,252
Retiree Health and Welfare Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of period	241	237
Service cost	1	1	1
Interest cost	8	9	10
Plan participants' contributions	4	4
Actuarial loss (gain)	(22)	14
Benefits Paid	(19)	(23)
Plan amendment	0	(1)
Projected benefit obligation at end of period	$ 213	$ 241	$ 237