Derivative Instruments and Hedging Activities (Summary Of Accumulated Other Comprehensive Loss Related To Derivatives) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
After-Tax Amount
Balance beginning of period	$ 2,993.5	$ 3,095.3
Net losses reclassified from accumulated other comprehensive loss into income	3.6	4.3
Balance end of period	3,019.0	$ 3,119.4
Deferred Net Gains (Losses) on Derivatives
Before-Tax Amount
Accumulated derivative net losses as the beginning of the period	1.6
Net changes in fair value of derivatives	(5.1)
Net losses reclassified from accumulated other comprehensive loss into income	0.6
Accumulated derivative net losses as of the end of the period	(2.9)
Income Tax
Accumulated derivative net losses as of the beginning of the period	0.2
Net changes in fair value of derivatives	(0.4)
Net losses reclassified from accumulated other comprehensive loss into income	0.0
Accumulated derivative net losses as of the end of the period	(0.2)
After-Tax Amount
Balance beginning of period	1.4
Net changes in fair value of derivatives	(4.7)
Net losses reclassified from accumulated other comprehensive loss into income	0.6
Balance end of period	$ (2.7)