Fair Value Measurements (Fair Value Of Notes Payable) (Details) - USD ($) $ in Millions		Jun. 30, 2016		Dec. 31, 2015		Jun. 30, 2015
Carrying Value		$ 2,480.8		$ 2,724.7
Fixed rate notes payable
Carrying Value		2,274.1		2,273.3
Estimated Fair Value		2,438.3		2,358.8
Floating rate notes payable (1)
Carrying Value		206.7	[1]	451.4	[1]	$ 390.4
Estimated Fair Value	[1]	$ 199.8		$ 441.3

[1] Includes balances outstanding under our unsecured credit facility and unsecured short-term borrowings.