Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- Definition

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13476-108611

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Fair Value Measurements - Additional Information (Detail) $ in Millions, € in Billions, ¥ in Billions	6 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)	Mar. 31, 2018 EUR (€)	Mar. 31, 2018 JPY (¥)	Sep. 30, 2017 EUR (€)	Sep. 30, 2017 JPY (¥)
Derivative [Line Items]
Unrealized gains on marketable common stock	$ 15	$ 10
Unrealized losses on marketable common stock	13	6
Fair value of long term debt	11,200	12,700
Fair Value, Inputs, Level 1 [Member]
Derivative [Line Items]
Fair value of long term debt	9,100	8,600
Fair Value, Inputs, Level 2 [Member]
Derivative [Line Items]
Fair value of long term debt	$ 2,100	$ 4,100
Foreign Currency Denominated Debt [Member]
Derivative [Line Items]
Notional amount \| ¥				¥ 35		¥ 35
Foreign Currency Denominated Debt [Member] \| One billion euro net investment hedge [Member]
Derivative [Line Items]
Notional amount \| €			€ 1		€ 1