Commitments and contingencies.

No definition available.

Name:	awk_CommitmentsAndContingenciesLineItems
Namespace Prefix:	awk_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Loss Contingency Accrual, Net of Tax

+ References

No definition available.

+ Details

Name:	awk_LossContingencyAccrualNetOfTax
Namespace Prefix:	awk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Loss Contingency, Cost Cap For Proposed Facilities

+ References

No definition available.

+ Details

Name:	awk_LossContingencyCostCapForProposedFacilities
Namespace Prefix:	awk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Loss Contingency, Cost Cap For Proposed Facilities, Increase

+ References

No definition available.

+ Details

Name:	awk_LossContingencyCostCapForProposedFacilitiesIncrease
Namespace Prefix:	awk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Loss Contingency, Estimate Of The Future Contribution

+ References

No definition available.

+ Details

Name:	awk_LossContingencyEstimateOfTheFutureContribution
Namespace Prefix:	awk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Loss Contingency, Natural Gas Outage Inconvenience Per Household, Amount

+ References

No definition available.

+ Details

Name:	awk_LossContingencyNaturalGasOutageInconveniencePerHouseholdAmount
Namespace Prefix:	awk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Loss Contingency, Natural Gas Outage Inconvenience Per Household, Average Amount Paid

+ References

No definition available.

+ Details

Name:	awk_LossContingencyNaturalGasOutageInconveniencePerHouseholdAverageAmountPaid
Namespace Prefix:	awk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Loss Contingency, Number of Agreements

+ References

No definition available.

+ Details

Name:	awk_LossContingencyNumberOfAgreements
Namespace Prefix:	awk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Loss Contingency, Number of Agreements, Valid

+ References

No definition available.

+ Details

Name:	awk_LossContingencyNumberOfAgreementsValid
Namespace Prefix:	awk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Loss Contingency, Number of Agreements, Void

+ References

No definition available.

+ Details

Name:	awk_LossContingencyNumberOfAgreementsVoid
Namespace Prefix:	awk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Loss Contingency, Number of Recommended Operational Improvements

+ References

No definition available.

+ Details

Name:	awk_LossContingencyNumberOfRecommendedOperationalImprovements
Namespace Prefix:	awk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Loss Contingency, Pending Claims, Number of Answers Provided For

+ References

No definition available.

+ Details

Name:	awk_LossContingencyPendingClaimsNumberOfAnswersProvidedFor
Namespace Prefix:	awk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Customer Affected By Loss of Natural Gas Service

+ References

No definition available.

+ Details

Name:	awk_NumberOfCustomerAffectedByLossOfNaturalGasService
Namespace Prefix:	awk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Customer Serving

+ References

No definition available.

+ Details

Name:	awk_NumberOfCustomerServing
Namespace Prefix:	awk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number Of Customers For Whom A Precautionary Boil Water Advisory Was Issued To

+ References

No definition available.

+ Details

Name:	awk_NumberOfCustomersForWhomAPrecautionaryBoilWaterAdvisoryWasIssuedTo
Namespace Prefix:	awk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of customers for whom system was reconfigured to maintain service while a final repair was completed.

+ References

No definition available.

+ Details

Name:	awk_NumberOfCustomersForWhomSystemWasReconfiguredToMaintainServiceWhileFinalRepairWasCompleted
Namespace Prefix:	awk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of customers impacted due to failure of main that caused water outages and low pressure.

+ References

No definition available.

+ Details

Name:	awk_NumberOfCustomersImpactedDueToFailureOfMainThatCausedThatWaterOutagesAndLowPressure
Namespace Prefix:	awk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Customers Who Completed Claim Process

+ References

No definition available.

+ Details

Name:	awk_NumberOfCustomersWhoCompletedClaimProcess
Namespace Prefix:	awk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Focused General Investigations

+ References

No definition available.

+ Details

Name:	awk_NumberOfFocusedGeneralInvestigations
Namespace Prefix:	awk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of impacted customers to which service was restored.

+ References

No definition available.

+ Details

Name:	awk_PercentageOfImpactedCustomersToWhichServiceWasRestored
Namespace Prefix:	awk_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Potential Condemnation, Asset Value

+ References

No definition available.

+ Details

Name:	awk_PotentialCondemnationAssetValue
Namespace Prefix:	awk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Potential Condemnation, Number of Statutory Standards Incorrectly Applied By Agency

+ References

No definition available.

+ Details

Name:	awk_PotentialCondemnationNumberOfStatutoryStandardsIncorrectlyAppliedByAgency
Namespace Prefix:	awk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Potential Condemnation, Offer Rejection Amount

+ References

No definition available.

+ Details

Name:	awk_PotentialCondemnationOfferRejectionAmount
Namespace Prefix:	awk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Potential Condemnation, Parcels of Land

+ References

No definition available.

+ Details

Name:	awk_PotentialCondemnationParcelsOfLand
Namespace Prefix:	awk_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Public Utilities, Aggregate Costs

+ References

No definition available.

+ Details

Name:	awk_PublicUtilitiesAggregateCosts
Namespace Prefix:	awk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Public Utilities, Allowance for Funds Used During Construction

+ References

No definition available.

+ Details

Name:	awk_PublicUtilitiesAllowanceForFundsUsedDuringConstruction
Namespace Prefix:	awk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Public Utility, Approved Cost Estimates

+ References

No definition available.

+ Details

Name:	awk_PublicUtilityApprovedCostEstimates
Namespace Prefix:	awk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Public Utility, Approved Recovery Amount

+ References

No definition available.

+ Details

Name:	awk_PublicUtilityApprovedRecoveryAmount
Namespace Prefix:	awk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Public Utility, Daily Production, Number of Gallons Related to Desalinated Water

+ References

No definition available.

+ Details

Name:	awk_PublicUtilityDailyProductionNumberOfGallonsRelatedToDesalinatedWater
Namespace Prefix:	awk_
Data Type:	dtr-types1:volumeItemType
Balance Type:	na
Period Type:	instant

- Definition

Public Utility, Initial Daily Production, Number of Gallons Related to Desalinated Water

+ References

No definition available.

+ Details

Name:	awk_PublicUtilityInitialDailyProductionNumberOfGallonsRelatedToDesalinatedWater
Namespace Prefix:	awk_
Data Type:	dtr-types1:volumeItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount awarded to other party in judgment or settlement of litigation.

+ References

No definition available.

+ Details

Name:	us-gaap_LitigationSettlementAmountAwardedToOtherParty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of loss contingency liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-1

Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-10

+ Details

Name:	us-gaap_LossContingencyAccrualAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of claims dismissed.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-4

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-9

+ Details

Name:	us-gaap_LossContingencyClaimsDismissedNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 720
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483359/720-20-50-1

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 27
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482395/460-10-55-27

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-9

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 450
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483076/450-20-50-4

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-3

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482425/460-10-50-2

+ Details

Name:	us-gaap_LossContingencyEstimateOfPossibleLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of pending claims pertaining to a loss contingency.

+ References

+ Details

Name:	us-gaap_LossContingencyPendingClaimsNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	dei_LegalEntityAxis=awk_CaliforniaAmericanWaterCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=awk_DunbarMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=awk_WestVirginiaAmericanWaterCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=stpr_WV
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAgencyAxis=awk_PublicServiceCommissionOfWestVirginiaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=awk_MountaineerGasCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=awk_MountaineerGasCompanyAndWestVirginiaAmericanWaterCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=awk_MontereyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RegulatoryAgencyAxis=awk_StateWaterResourcesControlBoardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Commitments and Contingencies (Details) gal in Millions			3 Months Ended
Commitments and Contingencies (Details) gal in Millions	Jan. 17, 2025 USD ($)	Apr. 24, 2024 claim	Dec. 31, 2024 USD ($) customer	Apr. 30, 2025 lawsuit	Apr. 10, 2025 USD ($)	Mar. 31, 2025 USD ($)	Jul. 24, 2024 improvement	Jun. 14, 2024 lawsuit	Feb. 19, 2024 lawsuit	Jan. 30, 2024 lawsuit	Dec. 20, 2023 lawsuit	Dec. 11, 2023 standard	Dec. 06, 2023 USD ($)	Nov. 16, 2023 investigation	Nov. 11, 2023 customer	Nov. 10, 2023 customer	Apr. 28, 2023 USD ($)	Dec. 05, 2022 USD ($)	Oct. 31, 2022 gal	Feb. 28, 2021 parcel	Dec. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2015 agreement	Jun. 30, 2015 customer	Jun. 27, 2015	Jun. 26, 2015	Jun. 23, 2015 customer
Commitments And Contingencies [Line Items]
Loss contingency, probable loss						$ 17,000,000
Daily production, number of gallons related to desalinated water \| gal																			6.4
Initial daily production, number of gallons related to desalinated water \| gal																			4.8
Number of dismissed claims \| claim		1
Cal Am
Commitments And Contingencies [Line Items]
Number of agreements, void \| agreement																								4
Number of agreements \| agreement																								5
Number of agreements, valid \| agreement																								1
Dunbar \| WVAWC
Commitments And Contingencies [Line Items]
Loss contingency, probable loss			$ 5,000,000
Number of customers impacted due to failure of main that caused water outages and low pressure \| customer																												25,000
Percentage of impacted customers to which service was restored																										20.00%	80.00%
Number of customers for whom system was reconfigured to maintain service while a final repair was completed \| customer																									3,000
Litigation settlement, proposed maximum pre-tax amount	$ 18,000,000
Estimate of the future contribution	5,000,000
Loss contingency, probable loss, net of tax			$ 3,900,000
West Virginia \| WVPSC
Commitments And Contingencies [Line Items]
Number of focused general investigations \| investigation														2
West Virginia \| WVAWC
Commitments And Contingencies [Line Items]
Number of customers for whom a precautionary boil water advisory was issued to \| customer															300
Number of customers who completed claim process \| customer			594
Natural gas outage inconvenience per household, average amount paid			$ 1,500
West Virginia \| Mountaineer Gas Company
Commitments And Contingencies [Line Items]
Number of customers serving \| customer																220,000
Number of customers affected by loss of natural gas service \| customer																1,500
West Virginia \| Mountaineer Gas Company and WVAWC
Commitments And Contingencies [Line Items]
Number of pending lawsuits \| lawsuit								4	4	4
Number of pending lawsuits with answers provided for \| lawsuit											3
Number of recommended operational improvements \| improvement							3
West Virginia \| Mountaineer Gas Company and WVAWC \| Subsequent Event
Commitments And Contingencies [Line Items]
Number of pending lawsuits \| lawsuit				4
Monterey \| Cal Am
Commitments And Contingencies [Line Items]
Potential condemnation, asset value																					$ 513,000,000
Potential condemnation, parcels of land \| parcel																				58
Potential condemnation, number of statutory standards incorrectly applied by agency \| standard												2
Potential condemnation, offer rejection amount																	$ 448,800,000
Monterey \| Cal Am \| SWRCB
Commitments And Contingencies [Line Items]
Approved cost estimates																						$ 279,000,000
Aggregate costs						290,000,000
Allowance for funds used during construction						92,000,000
Cost cap for proposed facilities, final																		$ 62,000,000
Monterey \| Cal Am \| SWRCB \| Subsequent Event
Commitments And Contingencies [Line Items]
Cost cap for extraction wells					$ 11,000,000
Maximum
Commitments And Contingencies [Line Items]
Loss contingency, possible loss						$ 4,000,000
Maximum \| Dunbar \| WVAWC
Commitments And Contingencies [Line Items]
Estimate of the future contribution	$ 5,000,000
Maximum \| West Virginia \| WVAWC
Commitments And Contingencies [Line Items]
Natural gas outage inconvenience per household, amount													$ 2,000
Maximum \| Monterey \| Cal Am \| SWRCB
Commitments And Contingencies [Line Items]
Approved recovery amount																		$ 112,000,000					$ 50,000,000