v3.4.0.3
Equity And Earnings Per Share (Narrative) (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 36 Months Ended 60 Months Ended 107 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2010
Dec. 31, 2015
Mar. 31, 2016
May. 03, 2007
Equity And Earnings Per Share [Line Items]            
IBG Inc. ownership % of IBG LLC 15.70%       15.70% 10.00%
IBG Holdings ownership % of IBG LLC 84.30%       84.30% 90.00%
IBG Holdings Redemption of IBG LLC           10.00%
IBG Holdings LLC Ownership Percentage of Class B Common Stock           100.00%
Preferred stock shares authorized 10,000     10,000 10,000  
Preferred stock shares issued 0     0 0  
Preferred stock shares outstanding 0     0 0  
Amortization period DTA (years) 15 years          
Unamortized deferred tax asset arising from equity offerings $ 282     $ 288 $ 282  
Percent of tax savings owed to IBG Holdings LLC 85.00%          
Percentage of tax savings retained by IBG Inc. 15.00%          
Deferred tax asset from common stock offerings $ 460       460  
Tax savings owed to IBG Holdings LLC 391       391  
Tax savings retained by IBG Inc. 69       69  
Tax savings paid to IBG Holdings LLC         99  
Shares reserved for future issuance           360,000,000
Shares redeemed by IBG Holdings from IBG LLC     5,013,259      
Cash Redemptions IBG Holdings     $ 114      
Fair Value Of Issued Shares For Membership Exchange $ 306       $ 306  
Shares Issued       11,047,295    
Thomas Peterffy and Affiliates Ownership 88.70%       88.70% 84.60%
Distribution from IBG LLC $ 42          
Cash distribution to IBG, Inc. $ 7          
Dividend per share $ 0.10          
Dividends paid to common shareholders $ 7 $ 6        
Declaration Date Apr. 19, 2016          
Payment Date Jun. 14, 2016          
Record Date Jun. 01, 2016          
Common Class A            
Equity And Earnings Per Share [Line Items]            
Common stock, par value $ 0.01     $ 0.01 $ 0.01  
Shares authorized 1,000,000,000     1,000,000,000 1,000,000,000  
Common stock, shares issued 64,123,982     64,121,150 64,123,982  
Common stock, shares outstanding 63,989,156     63,985,335 63,989,156  
Common Class B            
Equity And Earnings Per Share [Line Items]            
Shares authorized 100     100 100  
Common stock, shares issued 100     100 100  
Common stock, shares outstanding 100     100 100