Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 16	$ 14	$ 63	$ 41
Interest cost on projected benefit obligation	24	22	89	66
Expected return on plan assets	(30)	(32)	(122)	(96)
Amortization of unrecognized loss	9	9	30	22
Net periodic benefit cost	19	13	60	33
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	6	5	14	14
Interest cost on projected benefit obligation	10	7	27	22
Amortization of prior service cost/(credit)	(2)	(1)	(7)	(3)
Amortization of unrecognized loss		1	1	6
Net periodic benefit cost	$ 14	$ 12	$ 35	$ 39