Debt instrument maturity year.

No definition available.

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- Definition

Derivative Net Gain Amortized Through Interest

+ References

No definition available.

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- Definition

Derivative Notional Amount, Per Contract

+ References

No definition available.

+ Details

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- Definition

Derivative, Number of Instruments Terminated

+ References

No definition available.

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- Definition

Ineffectiveness Recognized on Hedge Instruments

+ References

No definition available.

+ Details

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- Definition

Proceeds Received From (Payment Due To) Terminated Forward Swaps

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
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Balance Type:	credit
Period Type:	instant

- 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

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- 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

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- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Average fixed interest rate related to the group of interest rate derivatives.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
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-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

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Balance Type:	na
Period Type:	instant

- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
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- 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

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Balance Type:	debit
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- Definition

The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3291-108585

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Long-Term Debt - Additional Information (Details)			1 Months Ended	3 Months Ended		9 Months Ended
Long-Term Debt - Additional Information (Details)	Apr. 14, 2020 USD ($)	Apr. 08, 2020 USD ($) treasury_lock_agreement	Mar. 31, 2020 USD ($) treasury_lock_agreement	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019
Debt Instrument [Line Items]
Proceeds from long-term debt						$ 1,250,000,000	$ 1,191,000,000
Fair value hedge ineffectiveness				$ 0	$ 0	0	$ 0
Designated as Hedging Instrument \| Treasury lock agreements
Debt Instrument [Line Items]
Derivative, number of instruments held \| treasury_lock_agreement			4
Debt instrument, term			10 years
Derivative notional amount, per contract			$ 100,000,000
Derivative, average fixed rate			0.94%
Derivative, number of instruments terminated \| treasury_lock_agreement		4
Derivate instrument notional amount		$ 400,000,000
Proceeds received from (payment due to) terminated forward swaps		$ (6,000,000)
Various debt
Debt Instrument [Line Items]
Proceeds from long-term debt						$ 250,000,000
Various debt maturing in 2020 through 2048
Debt Instrument [Line Items]
Weighted average interest rate on short-term debt				0.98%		0.98%
Various debt maturing in 2020 through 2048
Debt Instrument [Line Items]
Weighted average interest rate on short-term debt				5.31%		5.31%
American Water Capital Corp.
Debt Instrument [Line Items]
Weighted average interest rate on short-term debt				0.55%		0.55%		1.86%
Senior Notes \| American Water Capital Corp.
Debt Instrument [Line Items]
Debt instrument, face amount	$ 1,000,000,000.0
Proceeds from long-term debt	989,000,000
Repayments of debt	28,000,000
Senior Notes \| American Water Capital Corp. \| Senior Note 2.80% Due 2023
Debt Instrument [Line Items]
Debt instrument, face amount	$ 500,000,000
Interest rate	2.80%
Senior Notes \| American Water Capital Corp. \| Senior Note 3.45% Due 2050
Debt Instrument [Line Items]
Debt instrument, face amount	$ 500,000,000
Interest rate	3.45%
Minimum \| Designated as Hedging Instrument \| Treasury lock agreements
Debt Instrument [Line Items]
Derivative net gain amortized through interest		10 years
Minimum \| Various debt maturing in 2020 through 2048
Debt Instrument [Line Items]
Interest rate				0.00%		0.00%
Maturity date						2020
Minimum \| Various debt maturing in 2020 through 2048
Debt Instrument [Line Items]
Interest rate				0.00%		0.00%
Maturity date						2020
Maximum \| Various debt maturing in 2020 through 2048
Debt Instrument [Line Items]
Interest rate				5.00%		5.00%
Maturity date						2048
Maximum \| Various debt maturing in 2020 through 2048
Debt Instrument [Line Items]
Interest rate				12.25%		12.25%
Maturity date						2048
Debt instrument, redemption, period one
Debt Instrument [Line Items]
Repayments of debt						$ 266,000,000