Pension and Other Postretirement Benefits (Schedule Of Changes In Plan Assets And Projected Benefit Obligations Recognized In Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan
Net prior service cost/(credit)			$ 0.2	$ 0.9
Net actuarial (gain)/loss			127.5	(76.1)
Settlements	$ (18.5)	$ (13.7)	(18.5)	(13.7)	$ 0.0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	0.4	0.7	0.4	0.7	0.2
Less: amortization of net actuarial (gain) loss	(40.6)	(52.9)	(40.6)	(52.9)	(61.2)
Total Recognized in Other Comprehensive Income or Regulatory Asset or Liability			69.0	(141.1)
Amount Recognized in Net Periodic Benefits Cost and Other Comprehensive Income or Regulatory Asset or Liability			83.8	(100.0)
Other Postretirement Benefits
Net prior service cost/(credit)			0.1	1.6
Net actuarial (gain)/loss			(5.0)	18.9
Settlements	0.0	0.0	0.0	0.0	0.0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	4.0	4.4	4.0	4.4	4.9
Less: amortization of net actuarial (gain) loss	$ (3.8)	$ (3.0)	(3.8)	(3.0)	$ (3.1)
Total Recognized in Other Comprehensive Income or Regulatory Asset or Liability			(4.7)	21.9
Amount Recognized in Net Periodic Benefits Cost and Other Comprehensive Income or Regulatory Asset or Liability			$ 2.8	$ 27.2