Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension settlement costs	$ 43
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	25	$ 13
Interest cost on projected benefit obligation	34	23
Expected return on plan assets	(48)	(28)
Amortization of unrecognized loss	8	11
Net periodic pension benefit cost, before settlement	19	19
Pension settlement costs	43
Net periodic benefit cost	62	19
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	5	3
Interest cost on projected benefit obligation	10	7
Amortization of prior service cost/(credit)	(2)	(2)
Net periodic benefit cost	$ 13	$ 8