v3.26.1
Investment in Master Trust - Investments and other assets and changes in net assets (Details) - Puerto Rico Group Savings Plan - USD ($)
12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Investment in Master Trust    
Percentage of plan's interest in the Master Trust 1.00%  
Investments at contract value    
Net assets available for benefits $ 31,846,060 $ 30,674,061
Net investment income 4,293,565 3,521,874
Net Assets:    
Beginning of year 30,674,061 29,996,708
End of year 31,846,060 30,674,061
Sanofi U.S. Group Savings Master Trust    
Investments at fair value    
Total investments at fair value 8,808,891,943 7,969,065,149
Investments at contract value    
Stable value fund 487,868,228 489,852,592
Net assets available for benefits 9,296,760,171 8,458,917,741
Net Appreciation in the value of investments 1,341,677,244 978,908,389
Dividends 1,689,256 1,860,132
Interest 16,171,561 16,180,920
Net investment income 1,359,538,061 996,949,441
Net transfers (521,695,631) (305,936,717)
Increase in Net Assets 837,842,430 691,012,724
Net Assets:    
Beginning of year 8,458,917,741 7,767,905,017
End of year 9,296,760,171 8,458,917,741
Sanofi U.S. Group Savings Master Trust | Self-directed brokerage accounts    
Investments at fair value    
Total investments at fair value 195,671,531 166,382,492
Sanofi U.S. Group Savings Master Trust | Common collective trust funds    
Investments at fair value    
Total investments at fair value 8,321,132,717 7,524,576,465
Sanofi U.S. Group Savings Master Trust | Domestic equities    
Investments at fair value    
Total investments at fair value 196,628,547 181,509,806
Sanofi U.S. Group Savings Master Trust | Fixed income securities    
Investments at fair value    
Total investments at fair value 58,038,372 54,099,426
Sanofi U.S. Group Savings Master Trust | Company stock    
Investments at fair value    
Total investments at fair value 37,420,776 42,496,960
Sanofi Puerto Rico Group Savings Plan's Interest in Sanofi U.S. Group Savings Master Trust    
Investments at fair value    
Total investments at fair value 30,002,648 27,957,151
Investments at contract value    
Stable value fund 1,659,514 2,560,048
Net assets available for benefits 31,662,162 30,517,199
Net Appreciation in the value of investments 4,220,061 3,418,388
Dividends 18,495 18,922
Interest 55,009 84,564
Net investment income 4,293,565 3,521,874
Net transfers (3,148,602) (2,874,623)
Increase in Net Assets 1,144,963 647,251
Net Assets:    
Beginning of year 30,517,199 29,869,948
End of year 31,662,162 30,517,199
Sanofi Puerto Rico Group Savings Plan's Interest in Sanofi U.S. Group Savings Master Trust | Common collective trust funds    
Investments at fair value    
Total investments at fair value 27,283,689 25,509,857
Sanofi Puerto Rico Group Savings Plan's Interest in Sanofi U.S. Group Savings Master Trust | Domestic equities    
Investments at fair value    
Total investments at fair value 1,876,200 1,659,939
Sanofi Puerto Rico Group Savings Plan's Interest in Sanofi U.S. Group Savings Master Trust | Fixed income securities    
Investments at fair value    
Total investments at fair value 366,393 298,895
Sanofi Puerto Rico Group Savings Plan's Interest in Sanofi U.S. Group Savings Master Trust | Company stock    
Investments at fair value    
Total investments at fair value $ 476,366 $ 488,460