Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension settlement costs		$ 43
Pension Costs/Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 24	25
Interest cost on projected benefit obligation	30	34
Expected return on plan assets	(50)	(48)
Amortization of unrecognized (gain) loss	7	8
Net periodic pension benefit cost, before settlement	11	19
Pension settlement costs		43
Net periodic benefit cost	11	62
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	5	5
Interest cost on projected benefit obligation	9	10
Amortization of prior service cost/(credit)	(2)	(2)
Amortization of unrecognized (gain) loss	1
Net periodic benefit cost	$ 13	$ 13