Share Capital Share Capital (Movements in Treasury Shares) (Details) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Statement of Partners' Capital [Abstract]
Beginning balance	42.7	40.2	50.7
Acquisition of common shares	21.8	11.3	1.6
Distribution of common shares	(9.6)	(7.0)	(7.5)
Common shares distributed to meet option exercises	(0.9)	(1.8)	(4.6)
Ending balance	54.0	42.7	40.2