Accounting Policies and Pronouncements (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable threshold period past due	30 days
MUD Receivables
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, accrued interest, after allowance for credit loss	$ 17.7	$ 19.7

Amount, after allowance for credit loss, of accrued interest on financing receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 3A
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL120267960-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121599878&loc=SL120267845-210446

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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

Threshold period for when financing receivable is considered past due, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Excludes threshold period past due to write off as uncollectible.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919253-210447

+ Details

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Balance Type:	na
Period Type:	instant

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