Share-Based Compensation (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Options exercised			501,173	100,000
Total intrinsic value of options exercised			$ 9.5	$ 1.4
Weighted average remaining life			3.7
Remaining weighted average contractual life (years) outstanding options	4.9		4.9
Remaining weighted average contractual life (years) exercisable options			3.7
Fair value of shares vested			11.0	10.1
Total compensation cost for option and share awards	3.3	2.9	9.5	9.1
Total capitalized compensation cost for option and share awards	0.3	0.2	0.9	0.7
Minimum [Member]
Exercise price range for options exercised during the period			$ 30.06
Maximum [Member]
Exercise price range for options exercised during the period			$ 62.32
2011 Share Incentive Plan [Member]
Common shares which could be granted pursuant to full value awards	2,600,000		2,600,000
Total fungible units to be issued	9,100,000		9,100,000
Units available under the 2011 Share Plan	5,800,000		5,800,000
Fungible units transferred from the 2002 Share Plan to the 2011 Share Plan	3,300,000		3,300,000
Fungible Units To Full Value Award Conversion Ratio			3.45 to 1.0
Expiration value of option right or other award			0.83
Options [Member]
Total unrecognized compensation cost related to unvested options which is expected to be amortized	1.6		1.6
Expected amortized period of unrecognized compensation expected to be recognized for share-based compensation plans			3
Share Awards and Vesting [Member]
Total unrecognized compensation cost related to unvested options which is expected to be amortized	$ 30.7		$ 30.7
Expected amortized period of unrecognized compensation expected to be recognized for share-based compensation plans			5