Retirement Plans (Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension settlement costs	$ 9	$ 15	$ 34	$ 77
Pension Costs/Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	22	26	70	76
Interest cost on projected benefit obligation	31	27	91	94
Expected return on plan assets	(45)	(43)	(143)	(139)
Amortization of unrecognized (gain) loss	4	6	17	23
Net periodic pension benefit cost	12	16	35	54
Pension settlement costs	9	15	34	77
Net periodic benefit cost	21	31	69	131
OPEB Costs [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	5	5	16	16
Interest cost on projected benefit obligation	9	11	28	30
Amortization of prior service cost/(credit)	(1)	(2)	(6)	(7)
Amortization of unrecognized (gain) loss		(1)	1
Net periodic benefit cost	$ 13	$ 13	$ 39	$ 39