Income Taxes - Reconciliation of Beginning and Ending Unrecognized Tax Benefits by Fiscal Year (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 2,488	$ 2,579	$ 2,234
Increases of unrecognized tax benefits related to prior years	10	34	66
Decreases of unrecognized tax benefits related to prior years	(143)	(386)	(83)
Increases of unrecognized tax benefits related to current year	350	326	376
Decreases related to settlements with taxing authorities	(19)	(63)	(12)
Reductions related to lapsing statute of limitations	(3)	(2)	(2)
Balance at end of period	$ 2,683	$ 2,488	$ 2,579

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
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-URI https://asc.fasb.org/extlink&oid=123427490&loc=SL37586934-109318

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-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

+ References

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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