Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 13	$ 13
Interest cost on projected benefit obligation	23	22
Expected return on plan assets	(28)	(32)
Amortization of unrecognized loss	11	7
Net periodic benefit cost	19	10
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	3	5
Interest cost on projected benefit obligation	7	7
Amortization of prior service cost/(credit)	(2)	(1)
Amortization of unrecognized loss		3
Net periodic benefit cost	$ 8	$ 14