Investments Allowance for Credit Losses - Summary of Allowance for Credit Losses (Details) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Finance Leases Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance leases and notes receivable individually evaluated for impairment	$ 33.4	$ 30.5
Notes Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance leases and notes receivable individually evaluated for impairment	$ 4.8	$ 10.8

The balance of financing receivables that were individually evaluated for impairment.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Name:	us-gaap_FinancingReceivableIndividuallyEvaluatedForImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant