v3.25.1
Short-Term Debt - Additional Information (Details) - USD ($)
 3 Months Ended 12 Months Ended
Mar. 31, 2025
Dec. 31, 2024
Short-term Debt [Line Items]    
Outstanding debt $ 1,000,000,000.0 $ 880,000,000
Short-term debt 999,000,000 879,000,000
Commercial Paper    
Short-term Debt [Line Items]    
Outstanding with maturities greater than three months $ 0 $ 0
American Water Capital Corp.    
Short-term Debt [Line Items]    
Weighted average interest rate on short-term debt 4.63% 4.65%
Revolving Credit Facility | Letter of Credit    
Short-term Debt [Line Items]    
Letters of credit, maximum borrowing capacity $ 150,000,000 $ 150,000,000
Outstanding with maturities greater than three months 0 $ 0
Revolving Credit Facility | American Water Capital Corp.    
Short-term Debt [Line Items]    
Letters of credit, maximum borrowing capacity 2,750,000,000  
Line of credit facility, accordion feature, increase limit 500,000,000  
Revolving Credit Facility | American Water Capital Corp. | Letter of Credit    
Short-term Debt [Line Items]    
Letters of credit, maximum borrowing capacity $ 150,000,000