Business Combinations and Acquisitions of Noncontrolling Interests Purchase of Additional Interests (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended
	Dec. 31, 2012 numberofsubsidiaries	Nov. 30, 2012 numberofsubsidiaries	Oct. 31, 2012	May 31, 2012 numberofsubsidiaries	Feb. 28, 2012 numberofsubsidiaries	Nov. 30, 2011 numberofsubsidiaries	Sep. 30, 2011 numberofsubsidiaries	Apr. 30, 2011 numberofsubsidiaries	Jan. 31, 2011 numberofsubsidiaries	Jan. 31, 2013 total settlement, cash [Member]	Dec. 31, 2012 total settlement, cash [Member]	Oct. 31, 2012 total settlement, cash [Member]	Feb. 28, 2012 total settlement, cash [Member]	Sep. 30, 2011 total settlement, cash [Member]	Apr. 30, 2011 total settlement, cash [Member]	Oct. 31, 2012 total settlement, Class A common stock [Member]	Feb. 28, 2012 total settlement, Class A common stock [Member]	Sep. 30, 2011 total settlement, Class A common stock [Member]	Apr. 30, 2011 total settlement, Class A common stock [Member]	Feb. 28, 2012 compensation expense, cash [Member]	Sep. 30, 2011 compensation expense, cash [Member]	Apr. 30, 2011 compensation expense, cash [Member]	Feb. 28, 2012 compensation expense, Class A common stock [Member]	Sep. 30, 2011 compensation expense, Class A common stock [Member]	Apr. 30, 2011 compensation expense, Class A common stock [Member]	Jan. 31, 2013 Purchase of additional interests, Cash [Member]	Dec. 31, 2012 Purchase of additional interests, Cash [Member]	May 31, 2012 Purchase of additional interests, Cash [Member]	Nov. 30, 2011 Purchase of additional interests, Cash [Member]	Sep. 30, 2011 Purchase of additional interests, Cash [Member]	Apr. 30, 2011 Purchase of additional interests, Cash [Member]	Jan. 31, 2011 Purchase of additional interests, Cash [Member]	May 31, 2012 Purchase of additional interests, Stock [Member]	Nov. 30, 2011 Purchase of additional interests, Stock [Member]	Sep. 30, 2011 Purchase of additional interests, Stock [Member]	Apr. 30, 2011 Purchase of additional interests, Stock [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Number of majority-owned subsidiaries	1	1		2	1	1	1	1	1
Acquisition of additional interests in majority-owned subsidiary	$ 7.2	$ 0.4		$ 6.6	$ 2.5	$ 6.8	$ 8.3	$ 5.6																		$ 2.0	$ 5.2	$ 6.0	$ 0.3	$ 4.5	$ 2.7	$ 25.0	$ 0.6	$ 6.5	$ 3.8	$ 3.0
Stock-based compensation awards, settlement					2.5					1.2	3.3	7.0	2.4	2.6	6.7	1.8	0.5	2.2	7.4
Deferred compensation expense	$ 2.5		$ 6.3		$ 1.7		$ 6.7	$ 1.3												$ 1.3	$ 3.6	$ 0.6	$ 0.4	$ 3.1	$ 0.7
Deferred compensation expense, service period, number of years	1 year		1 year		2 years 0 months 0 days		2 years	2 years