v2.4.0.8
Employee Incentive Plans (Narrative) (Details) (USD $)
In Millions, except Share data, unless otherwise specified
 0 Months Ended 6 Months Ended 86 Months Ended
May 03, 2007
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Apr. 24, 2014
Dec. 31, 2013
May 03, 2007
Dec. 31, 2006
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
ROI Dollar Unit Payable   $ 3.1   $ 3.1   $ 5.6    
Vested balance of ROI payable   3.1   3.1   5.6    
ROI dollar compensation expense   0.3 0.2          
Common Stock Shares issued under ROI Unit Stock Plan             1,271,009  
ROI Shares issued to IBG LLC             1,250,000  
2007 SIP shares issued under ROI Unit Stock Plan             21,009  
Fair value ROI Treasury Stock             38.1  
Fair Value ROI Accrual               17.8
Maximum shares of stock distributable under 2007 Stock Incentive Plan   20,000,000   20,000,000 30,000,000 20,000,000    
Increase in 2007 Stock Incentive Plan shares         10,000,000      
Shares granted to external directors       20,423        
2007 Stock Incentive Plan Compensation Expense   21.6 24.1          
Estimated Future 2007 Stock Incentive Plan Compensation Expense   $ 32.5   $ 32.5        
Percent Shares Forfeited Post Employment             50.00%  
Over Fifty Nine Percent Unvested Shares Eligible             100.00%  
Former employees vesting schedule (Years) 5 years              
Post employment vesting percentage (Years 1 - 4)             12.50%  
Post employment vesting percentage (Year 5)             50.00%  
Post employment shares distribution       173,457        
Incentive Plan Shares Distributed From Treasury [Member]
                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Shares Distributed       16,238        
2007 ROI Unit Stock Plan [Member]
                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Vesting Percentage   • 10% on the date of the IPO (or on the first anniversary of the IPO, in the case of U.S. ROI Unit holders who made the above-referenced elections after December 31, 2006); and• an additional 15% on each of the first six anniversaries of the date of the IPO, assuming continued employment with IBG, Inc. and compliance with other applicable covenants.            
2007 Stock Incentive Plan (Shares)
                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Vesting Percentage   • 10% on the first vesting date, which approximates the anniversary of the IPO; and• an additional 15% on each of the following six anniversaries of the first vesting, assuming continued employment with IBG, Inc. and compliance with non-competition and other applicable covenants.            
Shares Distributed   (2,434,794) [1]            
[1] Shares cumulatively distributed under the 2007 Stock Incentive Plan include 16,238 shares from Treasury representing shares acquired at the IPO to satisfy obligations under the 2007 ROI Unit Stock Plan.