Employment Benefit Plans Change in Benefit Obligation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of period	$ 2,320	$ 2,452
Service cost	46	48	$ 38
Interest cost	95	90	95
Actuarial loss (gain)	(55)	(111)
Benefits paid	(143)	(145)
Administrative expenses	0	(1)
Settlements	(16)	(13)
Projected benefit obligation at end of period	2,247	2,320	2,452
Component representing future salary increases	(102)	(146)
Accumulated benefit obligation at end of period	2,145	2,174
Retiree Health and Welfare Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of period	258	280
Service cost	1	1	1
Interest cost	10	10	11
Actuarial loss (gain)	(13)	(13)
Benefits paid	(24)	(25)
Plan participants' contributions	5	5
Projected benefit obligation at end of period	$ 237	$ 258	$ 280