Derivative Financial Instruments (Effect Of Cash Flow Hedges On Financial Statements) (Details) - Forward Starting Pay Fixed Swaps [Member] - Cash Flow Hedging [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Gain (Loss) Recognized In Other Comprehensive Income (Loss)	$ 0.0	$ (118.0)	$ 33.3	$ (99.7)
Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedge (loss) gain reclassified from accumulated other comprehensive loss	(3.4)	(1.5)	$ (6.6)	(3.0)
Net realized gains (losses) on financial instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedge (loss) gain reclassified from accumulated other comprehensive loss	$ 0.0	$ 0.0		$ (12.0)