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Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 31, 2021 | Mar. 31, 2020 | Mar. 31, 2021 | Mar. 31, 2020 | Sep. 30, 2020
Derivatives, Fair Value [Line Items] |  |  |  |  |
Companys hedged interest rate transactions |  |  | 3 years |  |
Deferred (losses) gains on derivative financial instruments | $ 3 | $ (23) | $ 6 | $ (20) |
Interest Rate Swap |  |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |  |
Outstanding hedge contracts | 820 |  | 820 |  | $ 820
Deferred gain (loss) on derivative financial instruments |  |  | (23) |  |
Deferred (losses) gains on derivative financial instruments |  |  |  |  | $ (29)
Unrealized pre-tax (losses) gains on derivative financial instruments |  |  | 8 | (25) |
Foreign Exchange Contract | Other Income (Expense) |  |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |  |
Realized foreign exchange forward contract gain (loss) |  |  | (2) | (2) |
Unrealized foreign exchange forward contract gain (loss) |  |  | 0 | $ (3) |
Sale |  |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |  |
Outstanding hedge contracts | 243 |  | 243 |  |
Purchase |  |  |  |  |
Derivatives, Fair Value [Line Items] |  |  |  |  |
Outstanding hedge contracts | $ 149 |  | $ 149 |  |

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- Definition Maximum period the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121549185&loc=d3e80748-113994 + Details
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- Definition Amount, after tax and reclassification, of gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e637-108580 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669646-108580 + Details
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