Share-Based Compensation (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended				3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Jun. 30, 2011 2011 Share Incentive Plan [Member]	Mar. 31, 2012 2011 Share Incentive Plan [Member]	Mar. 31, 2012 Options [Member] Y	Mar. 31, 2011 Options [Member]	Mar. 31, 2012 Share Awards and Vesting [Member] Y	Mar. 31, 2011 Share Awards and Vesting [Member]	Mar. 31, 2012 Minimum [Member] Options [Member]	Mar. 31, 2011 Minimum [Member] Options [Member]	Mar. 31, 2012 Maximum [Member] Options [Member]	Mar. 31, 2011 Maximum [Member] Options [Member]
Total fungible units to be issued			9,100,000	8,000,000
Units available under the 2011 Share Plan			5,800,000
Fungible units transferred from the 2002 Share Plan to the 2011 Share Plan			3,300,000
Fungible Units To Full Value Award Conversion Ratio			3.45
Expiration value of option right or other award			0.83
Common shares which could be granted pursuant to full value awards				2,300,000
Options exercised	180,650				200,000	200,000
Exercise price range for options exercised during the period									$ 30.06	$ 30.06	$ 48.02	$ 48.02
Total intrinsic value of options exercised during the period					$ 3.7	$ 3.7
Total unrecognized compensation cost related to unvested options which is expected to be amortized					1.1		43.3
Expected amortized period of unrecognized compensation expected to be recognized for share-based compensation plans					2		5
Remaining weighted average contractual life (years) outstanding options					4.4
Remaining weighted average contractual life (years) exercisable options					3.6
Vesting period of options, minimum, years							3
Vesting period of options, maximum, years							5
Options granted in current year	0
Share awards vesting period, years							5
Fair value of shares vested							12.7	10.6
Total compensation cost for option and share awards	3.2	2.9
Total capitalized compensation cost for option and share awards	$ 0.3	$ 0.3