Fair Value Measurements (Fair Value Of Notes Payable) (Details) - USD ($) $ in Millions		Mar. 31, 2016		Dec. 31, 2015		Mar. 31, 2015
Carrying Value		$ 2,765.8		$ 2,724.7
Fixed rate notes payable
Carrying Value		2,273.7		2,273.3
Estimated Fair Value		2,407.3		2,358.8
Floating rate notes payable (1)
Carrying Value		492.1	[1]	451.4	[1]	$ 208.8
Estimated Fair Value	[1]	$ 484.0		$ 441.3

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