Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84164817&loc=d3e45280-112737

Name:	us-gaap_CapitalLeaseObligations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Leases Narrative (Details) - USD ($) $ in Millions	6 Months Ended
Leases Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Lessee, Lease, Description [Line Items]
Document Period End Date	Mar. 31, 2020
Maximum
Lessee, Lease, Description [Line Items]
Lessee Leases, Term of Contract	9 years 8 months 12 days
Minimum [Member]
Lessee, Lease, Description [Line Items]
Lessee Leases, Term of Contract	1 month
Other current liabilities
Lessee, Lease, Description [Line Items]
Capital Lease Obligations		$ 11
Other Liabilities [Member]
Lessee, Lease, Description [Line Items]
Capital Lease Obligations		8
Sale Lease Back Transaction [Member] \| Avaya Private Cloud Services Business [Member]
Lessee, Lease, Description [Line Items]
Capital Lease Obligations	$ 9	$ 13