Long-Term Debt - Retired Through Sinking Fund Provisions, Optional Redemptions or Payments at Maturities (Details) $ in Millions	9 Months Ended
Sep. 30, 2018 USD ($)
Minimum \| Senior notes
Debt Instrument [Line Items]
Interest rate	3.75%
Maturity date	2028
Maximum \| Senior notes
Debt Instrument [Line Items]
Interest rate	4.20%
Maturity date	2048
Debt instrument, redemption, period one
Debt Instrument [Line Items]
Total retirements and redemptions	$ 330
Debt instrument, redemption, period one \| Senior notes
Debt Instrument [Line Items]
Total retirements and redemptions	$ 310
Debt instrument, redemption, period one \| Other American Water subsidiaries \| Mandatorily redeemable preferred stock
Debt Instrument [Line Items]
Interest rate	8.49%
Maturity date	2036
Total retirements and redemptions	$ 1
Debt instrument, redemption, period one \| Other American Water subsidiaries \| Mortgage bonds
Debt Instrument [Line Items]
Interest rate	9.13%
Maturity date	2021
Total retirements and redemptions	$ 1
Debt instrument, redemption, period one \| Other American Water subsidiaries \| Term loan
Debt Instrument [Line Items]
Maturity date	2021
Total retirements and redemptions	$ 2
Debt instrument, redemption, period one \| Minimum \| Senior notes
Debt Instrument [Line Items]
Interest rate	5.62%
Maturity date	2018
Debt instrument, redemption, period one \| Minimum \| Other American Water subsidiaries \| Term loan
Debt Instrument [Line Items]
Interest rate	4.83%
Debt instrument, redemption, period one \| Maximum \| Senior notes
Debt Instrument [Line Items]
Interest rate	6.22%
Maturity date	2022
Debt instrument, redemption, period one \| Maximum \| Other American Water subsidiaries \| Term loan
Debt Instrument [Line Items]
Interest rate	5.69%
Debt instrument, redemption, period one \| Fixed rate two \| Private activity bonds and government funded debt
Debt Instrument [Line Items]
Total retirements and redemptions	$ 1
Debt instrument, redemption, period one \| Fixed rate two \| Minimum \| Private activity bonds and government funded debt
Debt Instrument [Line Items]
Interest rate	1.79%
Maturity date	2021
Debt instrument, redemption, period one \| Fixed rate two \| Maximum \| Private activity bonds and government funded debt
Debt Instrument [Line Items]
Interest rate	2.90%
Maturity date	2031
Debt instrument, redemption, period one \| Fixed rate three \| Other American Water subsidiaries \| Private activity bonds and government funded debt
Debt Instrument [Line Items]
Total retirements and redemptions	$ 15
Debt instrument, redemption, period one \| Fixed rate three \| Minimum \| Other American Water subsidiaries \| Private activity bonds and government funded debt
Debt Instrument [Line Items]
Interest rate	0.00%
Maturity date	2018
Debt instrument, redemption, period one \| Fixed rate three \| Maximum \| Other American Water subsidiaries \| Private activity bonds and government funded debt
Debt Instrument [Line Items]
Interest rate	5.40%
Maturity date	2047

Debt instrument maturity year.

No definition available.

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Namespace Prefix:	awk_
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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

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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

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=109223946&loc=d3e3291-108585

+ Details

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- Details

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