Stock Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended			3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Mar. 31, 2012 Restricted Stock [Member]	Mar. 31, 2011 Restricted Stock [Member]	Dec. 31, 2011 Performance Share Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awarding of performance shares earned payable in cash						40.00%
Number of shares authorized for grant	12,500,000
Shares available for future issuance	1,911,768
Options Roll Forward
Shares outstanding under option, Beginning Balance	2,220,000
Weighted average exercise price, Beginning Balance	$ 29.36
Shares outstanding under option, Exercised	(602,000)
Shares outstanding under option, Exercised, Weighted average exercise price	$ 26.97
Shares outstanding under option, Ending Balance	1,618,000
Weighted average exercise price, Ending Balance	$ 30.19
Weighted average remaining contractual term	4.0		4.1
Aggregate intrinsic value, outstanding	$ 87.6		$ 76.3
Restricted stock compensation expense
Restricted stock expense				4.7	2.9
Restricted stock expense, net of tax				3.5	2.2
Status of nonvested restricted stock
Nonvested shares subject to restriction, Beginning Balance	1,430,000
Nonvested shares subject to restriction, weighted average exercise price	$ 39.02
Restricted shares granted to employees	327,000			326,638
Granted shares subject to restriction, weighted average exercise price	$ 78.27
Shares subject to restriction, Vested	(631,000)
Vested shares subject to restriction, weighted average exercise price	$ 26.42
Shares subject to restriction, Forfeited	(23,000)
Forfeited shares subject to restriction, weighted average exercise price	$ 42.49
Nonvested shares subject to restriction, Ending Balance	1,103,000
Nonvested shares subject to restriction, weighted average exercise price	$ 57.79
Awarding of performance shares earned payable in common stock						60.00%
Performance Share Plan Expense Associated with Liability		$ 10.6