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Short-Term Debt - Schedule of Company's Aggregate Credit Facility Commitments, Commercial Paper Limit, Letter of Credit Availability and Availability Capacity (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Short-term Debt [Line Items]
Total availability	$ 2,600	$ 2,600
Total availability	2,750	2,750
Outstanding debt	(1,590)	(880)
Outstanding debt	(1,674)	(962)
Remaining availability	1,010	1,720
Remaining availability	1,076	1,788
Revolving Credit Facility
Short-term Debt [Line Items]
Remaining availability	1,076	1,788
Revolving Credit Facility | Letters of Credit
Short-term Debt [Line Items]
Total availability	150	150
Outstanding debt	(84)	(82)
Remaining availability	$ 66	$ 68

X

- Definition

Commercial Paper and Line of Credit Facility, Maximum Borrowing Capacity

+ References

No definition available.

+ Details

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Namespace Prefix:	awk_
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Balance Type:	credit
Period Type:	instant

X

- Definition

Commercial Paper and Line of Credit Facility, Outstanding

+ References

No definition available.

+ Details

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X

- Definition

Commercial Paper and Line of Credit Facility, Remaining Borrowing Capacity

+ References

No definition available.

+ Details

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Namespace Prefix:	awk_
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X

- Definition

Commercial Paper Maximum Borrowing Capacity

+ References

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- Definition

Commercial Paper Outstanding

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+ Details

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X

- Definition

Remaining borrowing capacity of commercial paper (current borrowing capacity less the amount of borrowings outstanding).

+ References

No definition available.

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Namespace Prefix:	awk_
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X

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 605
-Name Accounting Standards Codification
-Section 55
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477548/944-605-55-15

Reference 2: http://www.xbrl.org/2003/role/exampleRef
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-Name Accounting Standards Codification
-Section 55
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477548/944-605-55-12

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X

- 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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22)(b))
-Publisher FASB
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-Publisher FASB
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X

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
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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.

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No definition available.

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- Details

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