Allowance for Expected Credit Losses - Narrative (Details) $ in Millions	3 Months Ended
Mar. 31, 2020 USD ($) portfolio	Sep. 30, 2019
Credit Loss [Abstract]
Number of portfolio segments \| portfolio	2
Percentage of investment portfolio considered investment grade		99.00%
Interest income, accrual method \| $	$ 76

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

Name:	us-gaap_ImpairedFinancingReceivableInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration