Stock-Based Compensation (Details) (USD $) In Millions	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Stock-Based Compensation
Stock-based compensation expense (in dollars)	$ 11.0	$ 6.8
Stock Options | Directors
Stock-Based Compensation
Expiration period (in years)	ten years
Stock Options | Officers and Employees
Stock-Based Compensation
Number of share options granted during the period (in shares)	1.0	1.4
Expiration period (in years)	ten years
Vesting rights, annual increments for grants made prior to 2011 (as a percent)	25%
Vesting period for grants made prior to 2011 (in years)	four years
Expiration period for grants made prior to 2011 (in years)	ten years
Vesting rights, annual increments beginning on the grant date (as a percent)	25%
Vesting period (in years)	four years
Restricted Stock
Stock-Based Compensation
Expiration period (in years)	3 years
Number of restricted shares issued during the period (in shares)	0.8	0.5
Performance shares
Stock-Based Compensation
Number of restricted shares issued during the period (in shares)	0.8	0.5
Performance shares | Officers and Employees
Stock-Based Compensation
Awards granted, low end of range (in shares)	0
Awards granted, high end of range (in shares)	0.9
Percentage of vesting rights on the second anniversary of the grant date (as a percent)	75%
Percentage of vesting rights on the third anniversary of the grant date (as a percent)	25%