v3.26.1
Fair Value of Financial Information - Schedule of Measurements of Assets and Liabilities on Recurring Basis (Details) - USD ($)
$ in Millions
 6 Months Ended
Jun. 30, 2025
Jun. 30, 2026
Dec. 31, 2025
Assets:      
Restricted funds   $ 37 $ 41
Rabbi trust investments   36 32
Deposits   139 124
Mark-to-market derivative asset     2
Mark-to-market derivative asset [Extensible Enumeration Not Disclosed Flag] awk:DerivativeAssetStatementOfFinancialPositionExtensibleEnumerationNotDisclosedFlag    
Total assets   248 254
Liabilities:      
Deferred compensation obligations   39 38
Total liabilities   39 38
Total assets   209 216
Fixed-income securities      
Assets:      
Other investments   3 35
Money market and other      
Assets:      
Other investments   33 20
Level 1      
Assets:      
Restricted funds   37 41
Rabbi trust investments   36 32
Deposits   139 124
Mark-to-market derivative asset     0
Total assets   246 245
Liabilities:      
Deferred compensation obligations   39 38
Total liabilities   39 38
Total assets   207 207
Level 1 | Fixed-income securities      
Assets:      
Other investments   1 28
Level 1 | Money market and other      
Assets:      
Other investments   33 20
Level 2      
Assets:      
Restricted funds   0 0
Rabbi trust investments   0 0
Deposits   0 0
Mark-to-market derivative asset     2
Total assets   2 9
Liabilities:      
Deferred compensation obligations   0 0
Total liabilities   0 0
Total assets   2 9
Level 2 | Fixed-income securities      
Assets:      
Other investments   2 7
Level 2 | Money market and other      
Assets:      
Other investments   0 0
Level 3      
Assets:      
Restricted funds   0 0
Rabbi trust investments   0 0
Deposits   0 0
Mark-to-market derivative asset     0
Total assets   0 0
Liabilities:      
Deferred compensation obligations   0 0
Total liabilities   0 0
Total assets   0 0
Level 3 | Fixed-income securities      
Assets:      
Other investments   0 0
Level 3 | Money market and other      
Assets:      
Other investments   $ 0 $ 0