v3.26.3
Debt - Notes (Details) - Senior Notes
€ in Millions, $ in Millions
Sep. 17, 2026
USD ($)
May 31, 2026
USD ($)
Mar. 31, 2026
USD ($)
Jan. 31, 2026
USD ($)
Jan. 15, 2026
USD ($)
Jan. 15, 2026
EUR (€)
Dec. 31, 2025
USD ($)
Aon North America, Inc. And Aon Global Holdings PLC              
Debt Instrument [Line Items]              
Debt, face amount $ 13,500            
5.350 % Senior Notes Due 2029              
Debt Instrument [Line Items]              
Debt, face amount $ 2,000            
Debt interest rate percentage 5.35%            
5.625% Senior Notes Due 2031              
Debt Instrument [Line Items]              
Debt, face amount $ 3,000            
Debt interest rate percentage 5.625%            
5.800% Senior Notes Due 2033              
Debt Instrument [Line Items]              
Debt, face amount $ 2,000            
Debt interest rate percentage 5.80%            
5.950% Senior Notes Due 2036              
Debt Instrument [Line Items]              
Debt, face amount $ 2,750            
Debt interest rate percentage 5.95%            
6.100% Senior Notes Due 2038              
Debt Instrument [Line Items]              
Debt, face amount $ 1,000            
Debt interest rate percentage 6.10%            
6.450% Senior Notes Due 2046              
Debt Instrument [Line Items]              
Debt, face amount $ 750            
Debt interest rate percentage 6.45%            
6.450% Senior Notes Due 2056              
Debt Instrument [Line Items]              
Debt, face amount $ 2,000            
Debt interest rate percentage 6.45%            
Debt instrument, redemption price, percentage 101.00%            
2.850% Senior Notes Due May 2027              
Debt Instrument [Line Items]              
Debt, face amount   $ 600          
Debt interest rate percentage   2.85%          
5.125% Senior Notes Due March 2027              
Debt Instrument [Line Items]              
Debt, face amount     $ 600        
Debt interest rate percentage     5.125%        
8.205% Senior Notes Due January 2027              
Debt Instrument [Line Items]              
Debt, face amount       $ 521      
Debt interest rate percentage       8.205%      
2.875% Senior Notes Due May 2026              
Debt Instrument [Line Items]              
Debt, face amount         $ 593 € 500  
Debt interest rate percentage         2.875% 2.875%  
3.875% Senior Notes due December 2025              
Debt Instrument [Line Items]              
Debt, face amount             $ 750
Debt interest rate percentage             3.875%