Debt instrument maturity year.

No definition available.

Name:	awk_DebtInstrumentMaturityYear
Namespace Prefix:	awk_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow from a debt initially having maturity due after one year or beyond the operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=awk_PrivateActivityBondsAndGovernmentFundedDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=awk_PrivateActivityMortgageBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-Term Debt - Issued (Details) - USD ($) $ in Millions		12 Months Ended
Long-Term Debt - Issued (Details) - USD ($) $ in Millions	Apr. 14, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total issuances		$ 1,334	$ 1,530	$ 1,358
Other American Water subsidiaries \| Private activity bonds and government funded debt
Debt Instrument [Line Items]
Total issuances		$ 23
Other American Water subsidiaries \| Private activity bonds and government funded debt \| Minimum
Debt Instrument [Line Items]
Rate		0.00%
Maturity		2021
Other American Water subsidiaries \| Private activity bonds and government funded debt \| Maximum
Debt Instrument [Line Items]
Rate		5.00%
Maturity		2048
Other American Water subsidiaries \| Private activity bonds and government funded debt \| Weighted Average
Debt Instrument [Line Items]
Rate		0.16%
Other American Water subsidiaries \| Private activity mortgage bonds
Debt Instrument [Line Items]
Total issuances		$ 225
Other American Water subsidiaries \| Private activity mortgage bonds \| Minimum
Debt Instrument [Line Items]
Rate		0.85%
Maturity		2023
Other American Water subsidiaries \| Private activity mortgage bonds \| Maximum
Debt Instrument [Line Items]
Rate		1.20%
Maturity		2027
Other American Water subsidiaries \| Private activity mortgage bonds \| Weighted Average
Debt Instrument [Line Items]
Rate		1.10%
American Water Capital Corp. \| Senior notes
Debt Instrument [Line Items]
Total issuances	$ 989	$ 1,000
American Water Capital Corp. \| Senior notes \| Minimum
Debt Instrument [Line Items]
Rate		2.80%
Maturity		2030
American Water Capital Corp. \| Senior notes \| Maximum
Debt Instrument [Line Items]
Rate		3.45%
Maturity		2050
American Water Capital Corp. \| Senior notes \| Weighted Average
Debt Instrument [Line Items]
Rate		3.13%
American Water Capital Corp. \| Private activity bonds and government funded debt
Debt Instrument [Line Items]
Total issuances		$ 86
American Water Capital Corp. \| Private activity bonds and government funded debt \| Minimum
Debt Instrument [Line Items]
Rate		0.60%
Maturity		2023
American Water Capital Corp. \| Private activity bonds and government funded debt \| Maximum
Debt Instrument [Line Items]
Rate		0.70%
Maturity		2023
American Water Capital Corp. \| Private activity bonds and government funded debt \| Weighted Average
Debt Instrument [Line Items]
Rate		0.42%