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Regulatory Matters - Regulatory Assets and Liabilities Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Regulatory Asset And Liabilities [Line Items]
Regulatory asset, earned revenue, percentage	50.00%
Deferred pension expense
Regulatory Asset And Liabilities [Line Items]
Regulatory asset, underfunded status	$ 261	$ 304
Purchase premium recoverable through rates
Regulatory Asset And Liabilities [Line Items]
Regulatory asset, amortization period	40 years

X

- Definition

Defined benefit plan regulatory assets underfunded status.

+ References

No definition available.

+ Details

Name:	awk_DefinedBenefitPlanRegulatoryAssetsUnderfundedStatus
Namespace Prefix:	awk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Regulatory asset and liabilities.

+ References

No definition available.

+ Details

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

X

- Definition

Regulatory Asset, Earned Revenue, Percentage

+ References

No definition available.

+ Details

Name:	awk_RegulatoryAssetEarnedRevenuePercentage
Namespace Prefix:	awk_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Amortization period for the recovery of regulatory asset, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_RegulatoryAssetAmortizationPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_RegulatoryAssetAxis=us-gaap_PensionCostsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RegulatoryAssetAxis=awk_PurchasePremiumRecoverableThroughRatesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: