Employment Benefit Plans Net Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plan [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 48	$ 38	$ 47
Interest cost	90	95	89
Expected return on plan assets	(138)	(134)	(124)
Amortization of prior service credits	(1)	(1)	0
Amortization of net loss	2	1	17
Settlements	(1)	(1)	(1)
Net (benefit) cost recognized	0	(2)	28
Retiree Health and Welfare Benefits
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	1	1	1
Interest cost	10	11	12
Amortization of prior service credits	(2)	(2)	(1)
Amortization of net loss	2	1	5
Net (benefit) cost recognized	$ 11	$ 11	$ 17