v3.26.1
Shareholders' Equity - Schedule of Components of Accumulated Other Comprehensive Loss (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]        
Beginning balance $ 9,958 $ 7,195 $ 9,459 $ 6,305
Other comprehensive income (loss) before reclassifications, net     (197) 853
Amounts reclassified from accumulated other comprehensive income        
Amounts reclassified from accumulated other comprehensive income (loss)     72 66
Tax expense     (18) (17)
Amounts reclassified from accumulated other comprehensive income (loss), net     54 49
Total other comprehensive income (loss) attributable to Aon shareholders (58) 613 (143) 902
Ending balance 9,686 8,008 9,686 8,008
AOCI Attributable to Parent        
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]        
Beginning balance (3,928) (4,456) (3,843) (4,745)
Amounts reclassified from accumulated other comprehensive income        
Ending balance (3,986) (3,843) (3,986) (3,843)
Change in Fair Value of Financial Instruments        
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]        
Beginning balance     78 74
Other comprehensive income (loss) before reclassifications, net     (6) 17
Amounts reclassified from accumulated other comprehensive income        
Amounts reclassified from accumulated other comprehensive income (loss)     (4) (6)
Tax expense     1 2
Amounts reclassified from accumulated other comprehensive income (loss), net     (3) (4)
Total other comprehensive income (loss) attributable to Aon shareholders     (9) 13
Ending balance 69 87 69 87
Foreign Currency Translation Adjustments        
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]        
Beginning balance     (1,225) (2,051)
Other comprehensive income (loss) before reclassifications, net     (188) 843
Amounts reclassified from accumulated other comprehensive income        
Amounts reclassified from accumulated other comprehensive income (loss)     2 0
Tax expense     0 0
Amounts reclassified from accumulated other comprehensive income (loss), net     2 0
Total other comprehensive income (loss) attributable to Aon shareholders     (186) 843
Ending balance (1,411) (1,208) (1,411) (1,208)
Postretirement Benefit Obligation        
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]        
Beginning balance     (2,696) (2,768)
Other comprehensive income (loss) before reclassifications, net     (3) (7)
Amounts reclassified from accumulated other comprehensive income        
Amounts reclassified from accumulated other comprehensive income (loss)     74 72
Tax expense     (19) (19)
Amounts reclassified from accumulated other comprehensive income (loss), net     55 53
Total other comprehensive income (loss) attributable to Aon shareholders     52 46
Ending balance $ (2,644) $ (2,722) $ (2,644) $ (2,722)