EBPs Obligation Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plan, Defined Benefit [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	$ 1,544	$ 1,384
Service cost	59	40	$ 44
Interest cost	58	62	51
Plan participants' contributions	0	0
Benefits paid	(101)	(86)
Plan amendment	0	0
Actuarial loss (gain)	(91)	144
Settlements	(5)	(3)
Curtailments	0	0
Other	0	3
Benefit obligation at end of year	1,464	1,544	1,384
Other Postretirement Benefits [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	233	213
Service cost	2	2	2
Interest cost	9	10	11
Plan participants' contributions	2	2
Benefits paid	(13)	(14)
Plan amendment	0	1
Actuarial loss (gain)	(31)	21
Settlements	0	(1)
Curtailments	0	(1)
Other	0	0
Benefit obligation at end of year	$ 202	$ 233	$ 213