Income Taxes - Additional Information (Details) $ in Millions	3 Months Ended
Sep. 30, 2016 USD ($)
Income Tax Disclosure [Abstract]
Unrecognized tax benefits decreases in liability related to company's change in tax accounting method repairs and maintenance costs	$ 68

Unrecognized tax benefits decreases resulting from change in tax accounting method.

No definition available.

Name:	awk_UnrecognizedTaxBenefitsDecreasesResultingFromChangeInTaxAccountingMethod
Namespace Prefix:	awk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration