Regulatory Matters (Narrative) (Details)	12 Months Ended
Sep. 30, 2020
New York [Member]
Regulatory Matters [Line Items]
Approved Return on Equity	8.70%

Percentage of public utility's approved return on equity.

No definition available.

Name:	us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration