v3.26.1
Interest in Master Trust - Schedule of Master Trust Net Assets (Details) - EBP 003 - USD ($)
Dec. 31, 2025
Dec. 31, 2024
EBP, Master Trust [Line Items]    
Investments $ 8,041,513,805 $ 7,370,796,680
Dividends and interest receivable 13,890 28,299
Net assets available for benefits 8,075,715,079 7,405,052,698
Commingled Funds | Master Trust - Commingled Funds    
EBP, Master Trust [Line Items]    
Net assets available for benefits 4,447,738,227 4,050,028,950
Commingled Funds | Plan's Interest in Master Trust Commingled Funds    
EBP, Master Trust [Line Items]    
Net assets available for benefits 3,783,949,594 3,540,219,397
Marsh Stock Fund | Master Trust - Commingled Funds    
EBP, Master Trust [Line Items]    
Dividends and interest receivable 36,384 55,559
Liability for expenses incurred (21,253) (21,250)
Net assets available for benefits 580,295,140 737,638,443
Marsh Stock Fund | Plan's Interest in Master Trust Commingled Funds    
EBP, Master Trust [Line Items]    
Dividends and interest receivable 33,330 50,819
Liability for expenses incurred (19,469) (19,437)
Net assets available for benefits 531,584,790 674,707,696
Marsh common stock | Master Trust - Commingled Funds    
EBP, Master Trust [Line Items]    
Investments 569,666,803 722,475,231
Marsh common stock | Plan's Interest in Master Trust Commingled Funds    
EBP, Master Trust [Line Items]    
Investments 521,848,602 660,838,115
Short-term investment fund at fair value | Master Trust - Commingled Funds    
EBP, Master Trust [Line Items]    
Investments 10,613,206 15,128,903
Short-term investment fund at fair value | Plan's Interest in Master Trust Commingled Funds    
EBP, Master Trust [Line Items]    
Investments 9,722,327 13,838,199
Stable Value Fund | Master Trust - Commingled Funds    
EBP, Master Trust [Line Items]    
Investments 23,594,468 11,086,840
Security backed investment contracts at contract value 512,986,091 517,049,326
Dividends and interest receivable 85,026 43,260
Liability for expenses incurred (119,202) (118,452)
Net assets available for benefits 536,546,383 528,060,974
Stable Value Fund | Plan's Interest in Master Trust Commingled Funds    
EBP, Master Trust [Line Items]    
Investments 20,995,284 9,994,261
Security backed investment contracts at contract value 456,475,130 466,095,480
Dividends and interest receivable 75,659 38,997
Liability for expenses incurred (106,070) (106,779)
Net assets available for benefits 477,440,003 476,021,959
Common collective trusts at fair value | Master Trust - Commingled Funds    
EBP, Master Trust [Line Items]    
Net assets available for benefits 3,330,896,704 2,784,329,533
Common collective trusts at fair value | Plan's Interest in Master Trust Commingled Funds    
EBP, Master Trust [Line Items]    
Net assets available for benefits $ 2,774,924,801 $ 2,389,489,742