Retirement Plans (Assumptions Used) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Apr. 01, 2016
Pension Benefits [Member]
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - used at year end to value obligation (in hundredths)	3.70%	4.10%	4.50%	4.00%
Discount rate - used to compute annual cost (in hundredths)	4.10%	4.50%	4.10%
Expected long-term rate of return on plan assets (in hundredths)	7.50%	7.50%	7.75%
Rate of increase in compensation levels (in hundredths)	2.50%	2.50%	2.50%
Postretirement Benefits Other Than Pensions (OPEB) [Member] | Maximum [Member]
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - used at year end to value obligation (in hundredths)	3.80%	4.30%	4.70%
Discount rate - used to compute annual cost (in hundredths)	4.30%	4.70%	4.20%
Postretirement Benefits Other Than Pensions (OPEB) [Member] | Minimum [Member]
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - used at year end to value obligation (in hundredths)	3.70%	4.10%	4.50%
Discount rate - used to compute annual cost (in hundredths)	4.10%	4.50%	4.10%