Short-Term Debt - Additional Information (Details) - USD ($) $ in Millions |
6 Months Ended | 12 Months Ended |
|---|---|---|
Jun. 30, 2026 |
Dec. 31, 2025 |
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| Short-term Debt [Line Items] | ||
| Outstanding debt | $ 1,500 | $ 1,590 |
| Short-term debt | $ 1,499 | $ 1,588 |
| Short-Term Debt, Weighted Average Interest Rate, at Point in Time | 3.99% | 3.89% |
| Commercial Paper Program | ||
| Short-term Debt [Line Items] | ||
| Proceeds from short-term borrowings with maturities greater than three months | $ 0 | $ 0 |
| Revolving Credit Facility | Letters of Credit | ||
| Short-term Debt [Line Items] | ||
| Total availability | 150 | 150 |
| Proceeds from short-term borrowings with maturities greater than three months | $ 0 | 0 |
| Revolving Credit Facility | American Water Capital Corp. (AWCC) | ||
| Short-term Debt [Line Items] | ||
| Total availability | 2,750 | |
| Maximum commitment under the facility | $ 500 |
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition The cash inflow from a borrowing having initial term of repayment of more than three months but less than one year or one operating cycle (if the normal cycle is more than one year). Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Weighted average interest rate of short-term debt outstanding calculated at point in time. Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition Commercial Paper Outstanding No definition available.
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- Definition Line of Credit Facility, Accordion Feature, Increase Limit No definition available.
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