Employment Benefit Plans Change in Benefit Obligation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of period	$ 2,452	$ 2,220
Service cost	48	38	$ 47
Interest cost	90	95	89
Actuarial loss (gain)	(111)	256
Benefits paid	(145)	(141)
Administrative expenses	(1)	(1)
Settlements	(13)	(15)
Projected benefit obligation at end of period	2,320	2,452	2,220
Component representing future salary increases	(146)	(146)
Accumulated benefit obligation at end of period	2,174	2,306
Retiree Health and Welfare Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of period	280	272
Service cost	1	1	1
Interest cost	10	11	12
Actuarial loss (gain)	(13)	13
Benefits paid	(25)	(23)
Plan participants' contributions	5	6
Projected benefit obligation at end of period	$ 258	$ 280	$ 272