Stock Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended				3 Months Ended			9 Months Ended
	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2011 Restricted Stock [Member]	Mar. 31, 2011 Restricted Stock [Member]	Sep. 30, 2010 Restricted Stock [Member]	Sep. 30, 2011 Restricted Stock [Member]	Sep. 30, 2010 Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for grant	12,500,000
Shares available for future issuance	2,228,183
Options Roll Forward
Shares outstanding under option, Beginning Balance	2,569,000	2,777,000	3,253,000
Weighted average exercise price, Beginning Balance	$ 28.91	$ 28.69	$ 28.64
Shares outstanding under option, Exercised	(147,000)	(208,000)	(476,000)
Shares outstanding under option, Exercised, Weighted average exercise price	$ 26.34	$ 25.83	$ 28.4
Shares outstanding under option, Ending Balance	2,422,000	2,569,000	2,777,000
Weighted average exercise price, Ending Balance	$ 29.09	$ 28.91	$ 28.69
Weighted average remaining contractual term	4.3	4.5	4.7	4.9
Aggregate intrinsic value, outstanding	$ 76.2	$ 133.3	$ 141.6	$ 142.2
Restricted stock compensation expense
Restricted stock expense					3.4		5.0	11.0	15.4
Restricted stock expense, net of tax					$ 2.6		$ 3.7	$ 8.4	$ 12.0
Restricted stock expense net of tax per share - Basic					$ 0.02		$ 0.03	$ 0.08	$ 0.10
Restricted stock expense net of tax per share - Diluted					$ 0.02		$ 0.03	$ 0.07	$ 0.09
Status of nonvested restricted stock
Nonvested shares subject to restriction, Beginning Balance	1,507,100	1,556,300	1,870,600
Nonvested shares subject to restriction, weighted average exercise price	$ 38.98	$ 38.79	$ 30.55
Restricted shares granted to employees	1,000	3,288	270,144		3,288	270,144
Granted shares subject to restriction, weighted average exercise price	$ 71.66	$ 78.47	$ 70.47
Shares subject to restriction, Vested	(3,400)	(25,200)	(572,000)
Vested shares subject to restriction, weighted average exercise price	$ 44.38	$ 33.69	$ 27
Shares subject to restriction, Forfeited	(58,400)	(27,300)	(12,400)
Forfeited shares subject to restriction, weighted average exercise price	$ 37.75	$ 38.03	$ 30.14
Nonvested shares subject to restriction, Ending Balance	1,446,300	1,507,100	1,556,300
Nonvested shares subject to restriction, weighted average exercise price	$ 39.04	$ 38.98	$ 38.79