v3.26.3
Debt - Narrative (Details)
 9 Months Ended
Aug. 20, 2026
USD ($)
extension
Jul. 29, 2026
USD ($)
Sep. 30, 2026
USD ($)
Dec. 31, 2025
USD ($)
Line of Credit Facility [Line Items]        
Other short-term debt     $ 2,959,000,000 $ 1,035,000,000
India Subsidiaries        
Line of Credit Facility [Line Items]        
Maximum borrowing capacity     14,000,000  
Amount of debt outstanding     0  
Commercial Paper        
Line of Credit Facility [Line Items]        
Other short-term debt     $ 962,000,000 $ 1,035,000,000
Bridge Loan | Bridge Facility        
Line of Credit Facility [Line Items]        
Debt instrument, face amount $ 0 $ 6,200,000,000    
Debt instrument, term   364 days    
Revolving Credit Facility | Commercial Paper        
Line of Credit Facility [Line Items]        
Weighted average interest rate     4.20%  
Other short-term debt     $ 1,000,000,000.0  
Repayments of commercial paper     $ (73,000,000)  
Weighted average remaining maturity     20 days  
Revolving Credit Facility | Commercial Paper | Credit Facility        
Line of Credit Facility [Line Items]        
Other short-term debt     $ 1,000,000,000.0  
Revolving Credit Facility | Commercial Paper | Minimum        
Line of Credit Facility [Line Items]        
Debt instrument, term     1 year  
Revolving Credit Facility | Commercial Paper | Maximum        
Line of Credit Facility [Line Items]        
Debt instrument, term     28 years  
Senior Notes        
Line of Credit Facility [Line Items]        
Debt instrument, face amount 3,750,000,000   $ 22,300,000,000  
Debt instrument, term     12 years  
Weighted average interest rate     3.90%  
Debt issuance costs 47,000,000      
Net proceeds 3,700,000,000      
Senior Notes | 2029 Senior Notes (4.70%; due August 20, 2029)        
Line of Credit Facility [Line Items]        
Debt instrument, face amount $ 1,250,000,000      
Interest rate, stated percentage 4.70%   4.70%  
Net proceeds $ 2,300,000,000      
Senior Notes | 2031 Senior Notes (4.90%; due September 1, 2031)        
Line of Credit Facility [Line Items]        
Debt instrument, face amount $ 1,100,000,000      
Interest rate, stated percentage 4.90%   4.90%  
Senior Notes | 2033 Senior Notes (5.15%; due September 1, 2033)        
Line of Credit Facility [Line Items]        
Debt instrument, face amount $ 650,000,000      
Interest rate, stated percentage 5.15%   5.15%  
Senior Notes | 2036 Senior Notes (5.40%; due September 1, 2036)        
Line of Credit Facility [Line Items]        
Debt instrument, face amount $ 750,000,000      
Interest rate, stated percentage 5.40%   5.40%  
Line of Credit | Revolving Credit Facility | Credit Facility        
Line of Credit Facility [Line Items]        
Debt instrument, term 1 year      
Maximum borrowing capacity $ 3,670,000,000   $ 3,900,000,000  
Additional borrowing capacity     1,250,000,000  
Renewal options | extension 2      
Remaining borrowing capacity $ 230,000,000      
Amount of debt outstanding     0  
Currently available for borrowing     3,900,000,000  
Amount required to stop broker-dealer subsidiary commitments     168,000,000  
Funds available to use for working capital and general and corporate purposes     2,800,000,000  
Debt issuance costs 4,000,000      
Line of Credit | Revolving Credit Facility | Credit Facility | MarketAxess Holdings Inc.        
Line of Credit Facility [Line Items]        
Maximum borrowing capacity $ 1,500,000,000      
Line of Credit | Secured Debt | Term Loan        
Line of Credit Facility [Line Items]        
Debt instrument, term 24 months      
Debt issuance costs $ 2,000,000      
Term loan $ 2,000,000,000.0      
Proceeds from long-term lines of credit     $ 0