Stock Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended			12 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2013 Restricted Stock [Member]	Sep. 30, 2012 Restricted Stock [Member]	Sep. 30, 2013 Restricted Stock [Member]	Sep. 30, 2012 Restricted Stock [Member]	Sep. 30, 2013 Retiring named executive officers [Member]	Sep. 30, 2013 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	1,600,000
Options Roll Forward
Shares outstanding under option, Beginning Balance	1,154,000	1,355,000	1,436,000
Weighted average exercise price, Beginning Balance	$ 31.34	$ 30.78	$ 30.65
Shares outstanding under option, Exercised	(103,000)	(201,000)	(81,000)
Shares outstanding under option, Exercised, Weighted average exercise price	$ 30.12	$ 27.56	$ 28.43
Shares outstanding under option, Ending Balance	1,051,000	1,154,000	1,355,000	1,436,000
Weighted average exercise price, Ending Balance	$ 31.46	$ 31.34	$ 30.78	$ 30.65
Weighted average remaining contractual term	2 years 10 months	3 years 1 month	3 years 2 months	3 years 5 months
Aggregate intrinsic value, outstanding	$ 73.5	$ 63.2	$ 63.1	$ 58.8
Restricted stock compensation expense
Restricted stock compensation expense					$ 4.9	$ 5.0	$ 20.8	$ 14.9	$ 5.5
Status of nonvested restricted stock
Nonvested shares subject to restriction, Beginning Balance	992,000	1,054,000	1,032,000
Nonvested shares subject to restriction, weighted average exercise price	$ 67.37	$ 67.71	$ 58.77
Restricted shares granted to employees		15,000	372,000				373,197			14,140
Granted shares subject to restriction, weighted average exercise price		$ 75.32	$ 75.41
Shares subject to restriction, Vested	(6,000)	(65,000)	(331,000)
Vested shares subject to restriction, weighted average exercise price	$ 42.23	$ 72.93	$ 47.69
Shares subject to restriction, Forfeited	(21,000)	(12,000)	(19,000)
Forfeited shares subject to restriction, weighted average exercise price	$ 75.56	$ 75.68	$ 68.14
Nonvested shares subject to restriction, Ending Balance	965,000	992,000	1,054,000	1,032,000
Nonvested shares subject to restriction, weighted average exercise price	$ 67.36	$ 67.37	$ 67.71	$ 58.77