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=109223946&loc=d3e3255-108585

+ Details

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

- Details

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

- Details

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

- Details

Name:	awk_GovernmentProgramAxis=awk_NewJerseyEnvironmentalInfrastructureFinancingProgramMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-Term Debt - Issued (Details) - USD ($) $ in Millions		9 Months Ended
Long-Term Debt - Issued (Details) - USD ($) $ in Millions	Aug. 09, 2018	Sep. 30, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Total issuances	$ 1,300	$ 1,355	$ 1,382
Senior notes \| Fixed rate
Debt Instrument [Line Items]
Total issuances		$ 1,325
Senior notes \| Minimum
Debt Instrument [Line Items]
Interest rate		3.75%
Maturity date		2028
Senior notes \| Maximum
Debt Instrument [Line Items]
Interest rate		4.20%
Maturity date		2048
Private activity bonds and government funded debt \| Fixed rate
Debt Instrument [Line Items]
Total issuances		$ 30
Private activity bonds and government funded debt \| Minimum \| Fixed rate
Debt Instrument [Line Items]
Interest rate		0.00%
Maturity date		2020
Private activity bonds and government funded debt \| Maximum \| Fixed rate
Debt Instrument [Line Items]
Interest rate		5.00%
Maturity date		2048
New Jersey Environmental Infrastructure Financing Program
Debt Instrument [Line Items]
Total issuances		$ 26