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, 2024	Jun. 30, 2024
After-Tax Amount
Balance beginning of period	$ 4,755.2	$ 4,656.8
Balance end of period	4,053.9	4,053.9
Deferred Net (Losses) Gains on Derivatives
Before-Tax Amount
Accumulated derivative net gains (losses) as the beginning of the period	8.1	(1.3)
Net changes in fair value of derivatives	(2.8)	4.0
Net losses reclassified from accumulated other comprehensive loss into income	1.5	4.1
Accumulated derivative net gains (losses) as of the end of the period	6.8	6.8
Income Tax Expense (Benefit)
Accumulated derivative net gains (losses) as of the beginning of the period	2.0	(0.5)
Net changes in fair value of derivatives	0.7	2.9
Net losses reclassified from accumulated other comprehensive loss into income	0.0	0.3
Accumulated derivative net gains (losses) as of the end of the period	2.7	2.7
After-Tax Amount
Balance beginning of period	6.1	(0.8)
Other comprehensive loss before reclassifications	(3.5)	1.1
Net losses reclassified from accumulated other comprehensive loss into income	1.5	3.8
Balance end of period	$ 4.1	$ 4.1