Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Paragraph 1
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Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
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Amount of lessee's right to use underlying asset under operating lease.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
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New Accounting Pronouncements - Additional Information (Detail) - USD ($)	Mar. 31, 2019	Sep. 30, 2018
Five Year Unsecured Revolving Credit Facility [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Credit facility, borrowing capacity		$ 3,000,000,000
Scenario, Forecast [Member] \| Five Year Unsecured Revolving Credit Facility [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Credit facility, borrowing capacity	$ 3,000,000,000
Scenario, Forecast [Member] \| Minimum [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Lease assets	500,000,000
Lease liabilities	500,000,000
Scenario, Forecast [Member] \| Maximum [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Lease assets	750,000,000
Lease liabilities	$ 750,000,000