Derivative Instruments and Hedging Activities (Summary Of Accumulated Other Comprehensive Loss Related To Derivatives) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
After-Tax Amount
Balance beginning of period	$ 2,690.6	$ 3,019.0	$ 2,907.0	$ 2,993.5
Net gains reclassified from accumulated other comprehensive loss into income	0.3	3.5	3.7	7.1
Balance end of period	2,717.5	$ 3,128.7	2,717.5	$ 3,128.7
Deferred Net Gains (Losses) on Derivatives
Before-Tax Amount
Accumulated derivative net gains (losses) as the beginning of the period			(1.5)
Net changes in fair value of derivatives			9.2
Net gains reclassified from accumulated other comprehensive loss into income			(3.2)
Accumulated derivative net gains (losses) as of the end of the period	4.5		4.5
Income Tax
Accumulated derivative net gains (losses) as of the beginning of the period			(0.2)
Net changes in fair value of derivatives			1.0
Net gains reclassified from accumulated other comprehensive loss into income			0.0
Accumulated derivative net gains (losses) as of the end of the period	0.8		0.8
After-Tax Amount
Balance beginning of period			(1.3)
Net changes in fair value of derivatives			8.2
Net gains reclassified from accumulated other comprehensive loss into income			(3.2)
Balance end of period	$ 3.7		$ 3.7