Stock Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended			9 Months Ended	12 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Restricted Stock [Member]	Sep. 30, 2011 Restricted Stock [Member]	Sep. 30, 2012 Restricted Stock [Member]	Sep. 30, 2011 Restricted Stock [Member]	Sep. 30, 2012 Director [Member] 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	1,900,000
Options Roll Forward
Shares outstanding under option, Beginning Balance	1,587,000	1,618,000	2,220,000
Weighted average exercise price, Beginning Balance	$ 30.23	$ 30.19	$ 29.36
Shares outstanding under option, Exercised	(105,000)	(31,000)	(602,000)
Shares outstanding under option, Exercised, Weighted average exercise price	$ 27.26	$ 28.14	$ 26.97
Shares outstanding under option, Ending Balance	1,482,000	1,587,000	1,618,000		2,220,000
Weighted average exercise price, Ending Balance	$ 30.43	$ 30.23	$ 30.19		$ 29.36
Weighted average remaining contractual term	3 years 7 months	3 years 8 months	4 years		4 years 1 month
Aggregate intrinsic value, outstanding	$ 57.3	$ 56.1	$ 87.6		$ 76.3
Restricted stock compensation expense
Restricted stock expense						5.0	3.4	14.9	11.0
Restricted stock expense, net of tax						3.7	2.6	10.9	8.4
Status of nonvested restricted stock
Nonvested shares subject to restriction, Beginning Balance	1,085,000	1,103,000	1,430,000
Nonvested shares subject to restriction, weighted average exercise price	$ 58.47	$ 57.79	$ 39.02
Restricted shares granted to employees		11,000	327,000					328,138		9,677
Granted shares subject to restriction, weighted average exercise price		$ 82.33	$ 78.27
Shares subject to restriction, Vested	(8,000)	(25,000)	(631,000)
Vested shares subject to restriction, weighted average exercise price	$ 45.88	$ 38.82	$ 26.42
Shares subject to restriction, Forfeited	(21,000)	(4,000)	(23,000)
Forfeited shares subject to restriction, weighted average exercise price	$ 55.83	$ 58.72	$ 42.49
Nonvested shares subject to restriction, Ending Balance	1,056,000	1,085,000	1,103,000		1,430,000
Nonvested shares subject to restriction, weighted average exercise price	$ 58.62	$ 58.47	$ 57.79		$ 39.02
Performance Share Plan Expense Associated with Liability				$ 15.1