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=6877327&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=118932676&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:	us-gaap_DebtInstrumentAxis=awk_PrivateActivityBondsAndGovernmentFundedIssuedIn2017Member
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:	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:

- Details

Name:	us-gaap_DebtInstrumentAxis=awk_SeniorNotesIssuedIn2017Member
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	May 13, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Interest rate		2.45%
Total issuances		$ 1,530	$ 1,358	$ 1,395
Other American Water subsidiaries \| Private activity bonds and government funded debt \| Private Activity Bonds And Government Funded, Issued In 2017
Debt Instrument [Line Items]
Total issuances		$ 330
Other American Water subsidiaries \| Private activity bonds and government funded debt \| Minimum \| Private Activity Bonds And Government Funded, Issued In 2017
Debt Instrument [Line Items]
Interest rate		0.00%
Maturity date		2021
Other American Water subsidiaries \| Private activity bonds and government funded debt \| Maximum \| Private Activity Bonds And Government Funded, Issued In 2017
Debt Instrument [Line Items]
Interest rate		5.00%
Maturity date		2048
American Water Capital Corp. \| Senior notes
Debt Instrument [Line Items]
Total issuances	$ 1,090
American Water Capital Corp. \| Senior notes \| Senior Notes, Issued In 2017
Debt Instrument [Line Items]
Total issuances		$ 1,100
American Water Capital Corp. \| Senior notes \| Minimum \| Senior Notes, Issued In 2017
Debt Instrument [Line Items]
Interest rate		3.45%
Maturity date		2029
American Water Capital Corp. \| Senior notes \| Maximum \| Senior Notes, Issued In 2017
Debt Instrument [Line Items]
Interest rate		4.15%
Maturity date		2049
American Water Capital Corp. \| Private activity bonds and government funded debt
Debt Instrument [Line Items]
Maturity date		2039
Total issuances		$ 100