v3.26.1
Interest in Master Trust - Schedule of Master Trust Net Assets (Details) - EBP 006 - USD ($)
Dec. 31, 2025
Dec. 31, 2024
EBP, Master Trust [Line Items]    
Investments at fair value $ 1,899,264,477 $ 1,497,678,607
Accrued interest receivable 3,575 3,831
Net assets available for benefits 1,920,398,216 1,518,156,186
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 663,788,635 509,809,553
Marsh Stock Fund | Master Trust - Commingled Funds    
EBP, Master Trust [Line Items]    
Accrued 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]    
Accrued interest receivable 3,054 4,740
Liability for expenses incurred (1,784) (1,813)
Net assets available for benefits 48,710,350 62,930,747
Marsh common stock at fair value | Master Trust - Commingled Funds    
EBP, Master Trust [Line Items]    
Investments at fair value 569,666,803 722,475,231
Marsh common stock at fair value | Plan's Interest in Master Trust Commingled Funds    
EBP, Master Trust [Line Items]    
Investments at fair value 47,818,201 61,637,116
Short-term investment fund at fair value | Master Trust - Commingled Funds    
EBP, Master Trust [Line Items]    
Investments at fair value 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 at fair value 890,879 1,290,704
Stable Value Fund | Master Trust - Commingled Funds    
EBP, Master Trust [Line Items]    
Investments at fair value 23,594,468 11,086,840
Security backed investment contracts at contract value 512,986,091 517,049,326
Accrued 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 at fair value 2,599,185 1,092,579
Security backed investment contracts at contract value 56,510,961 50,953,846
Accrued interest receivable 9,367 4,263
Liability for expenses incurred (13,131) (11,673)
Net assets available for benefits 59,106,382 52,039,015
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 $ 555,971,903 $ 394,839,791