Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension settlement costs	$ 25	$ 19	$ 25	$ 62
Pension Costs/Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	24	25	48	50
Interest cost on projected benefit obligation	30	33	60	67
Expected return on plan assets	(48)	(48)	(98)	(96)
Amortization of unrecognized (gain) loss	6	9	13	17
Net periodic pension benefit cost	12	19	23	38
Pension settlement costs	25	19	25	62
Net periodic benefit cost	37	38	48	100
OPEB Costs [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	6	6	11	11
Interest cost on projected benefit obligation	10	9	19	19
Amortization of prior service cost/(credit)	(3)	(3)	(5)	(5)
Amortization of unrecognized (gain) loss		1	1	1
Net periodic benefit cost	$ 13	$ 13	$ 26	$ 26