Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 34	$ 14	$ 47	$ 27
Interest cost on projected benefit obligation	42	22	65	44
Expected return on plan assets	(65)	(32)	(92)	(64)
Amortization of unrecognized loss	11	6	21	13
Net periodic benefit cost	22	10	41	20
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	5	4	8	9
Interest cost on projected benefit obligation	10	8	17	15
Amortization of prior service cost/(credit)	(2)	(1)	(5)	(2)
Amortization of unrecognized loss		2	1	5
Net periodic benefit cost	$ 13	$ 13	$ 21	$ 27