v3.26.1
Investment in Master Trust - Fully Benefit-Responsive investment Contracts (Details) - U.S. Group Savings Plan - Sanofi U.S. Group Savings Master Trust - USD ($)
12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Investment in Master Trust    
Average crediting rate for the investment contracts 3.39% 3.39%
Redemption notice period (in years) 1 year  
Stable value fund $ 487,868,228 $ 489,852,592
Cash reserves common trust fund    
Investment in Master Trust    
Stable value fund 14,800,092 12,219,011
Synthetic investment contracts    
Investment in Master Trust    
Stable value fund $ 473,068,136 $ 477,633,581