Fair Value Measurements (Fair Value Of Notes Payable) (Details) - USD ($) $ in Millions		Sep. 30, 2020		Dec. 31, 2019		Sep. 30, 2019
Carrying Value		$ 3,225.8		$ 2,524.1
Fixed rate notes payable
Carrying Value		3,126.0		2,380.4
Estimated Fair Value		3,490.8		2,533.5
Floating rate notes payable (1)
Carrying Value		99.8	[1]	143.7	[1]	$ 99.7
Estimated Fair Value	[1]	$ 99.4		$ 143.8

[1] Includes balances outstanding under our unsecured credit facility at December 31, 2019.