Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension settlement costs	$ 19		$ 62
Pension Costs [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	25	$ 34	50	$ 47
Interest cost on projected benefit obligation	33	42	67	65
Expected return on plan assets	(48)	(65)	(96)	(92)
Amortization of unrecognized loss	9	11	17	21
Net periodic pension benefit cost, before settlement	19	22	38	41
Pension settlement costs	19		62
Net periodic benefit cost	38	22	100	41
Postretirement Benefits Other Than Pensions (OPEB) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	6	5	11	8
Interest cost on projected benefit obligation	9	10	19	17
Amortization of prior service cost/(credit)	(3)	(2)	(5)	(5)
Amortization of unrecognized loss	1		1	1
Net periodic benefit cost	$ 13	$ 13	$ 26	$ 21