The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

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Name:	us-gaap_ImpairmentOfLongLivedAssetsHeldForUse
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Summary of Significant Accounting Polices - PPNE, Impairment of Long-Lived Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Impairment of Long-Lived Assets
Impairment of long-lived assets	$ 0.0	$ 0.0	$ 0.0
Software \| Minimum
Property, Plant and Equipment
Property, plant and equipment, useful life	3 years
Software \| Maximum
Property, Plant and Equipment
Property, plant and equipment, useful life	7 years