Equity method investment ownership percentage sold.

No definition available.

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- Definition

Gain loss on investments net of tax.

+ References

No definition available.

+ Details

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- Definition

Gain (loss) on sale of equity investments net of tax and noncontrolling interest.

+ References

No definition available.

+ Details

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- Definition

Investment percentage.

+ References

No definition available.

+ Details

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- Definition

Number Of Refineries

+ References

No definition available.

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Balance Type:	na
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- Definition

Ownership interest in joint venture.

+ References

No definition available.

+ Details

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Balance Type:	na
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- Definition

Amount classified as assets attributable to disposal group held for sale or disposed of.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=64862545&loc=d3e2941-110230

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=65878427&loc=d3e1107-107759

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5B
-Subparagraph (e)
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=65878427&loc=SL51721533-107759

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Balance Type:	debit
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- Definition

The difference between the carrying value and the sale price of equity securities, not separately or otherwise categorized as trading or available-for-sale. This element includes investments in which the entity holds a small ownership stake (generally, less than 20% of the shares outstanding) and cannot exert significant influence.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13(h))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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- Definition

The net realized gain (loss) on investments sold during the period, not including gains (losses) on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity, which, for cash flow reporting, is a component of proceeds from investing activities.

+ References

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- Definition

The cash inflow associated with the sale, maturity and collection of all investments such as debt, security and so forth during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3179-108585

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Balance Type:	debit
Period Type:	duration

- Definition

The cash inflow associated with the sale of equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

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-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3179-108585

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- Definition

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.

+ References

No definition available.

+ Details

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- Details

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- Details

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- Details

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Investments - Additional Information (Detail) AUD in Millions, $ in Millions	1 Months Ended		9 Months Ended			12 Months Ended
	Apr. 30, 2016 USD ($) Refinery	Apr. 30, 2016 AUD Refinery	Sep. 30, 2016 USD ($)	Sep. 30, 2016 AUD	Sep. 30, 2015 USD ($)	Dec. 31, 2004	Dec. 31, 2015 USD ($)
Schedule of Equity Method Investments [Line Items]
Number of alumina refineries to be powered under supplied agreement \| Refinery	3	3
Sales of investments			$ 280		$ 40
Alcoa Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest in joint venture	60.00%	60.00%	25.10%	25.10%
Alumina Limited of Australia [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest in joint venture	40.00%	40.00%
AofA [Member]
Schedule of Equity Method Investments [Line Items]
Gain after tax and noncontrolling interest			$ 11	AUD 15
Pretax gain on sale of investments			27	AUD 35
AofA [Member] \| Dampier to Bunbury Natural Gas Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Investment percentage in DBP to be sold	20.00%	20.00%
Amount to be received by sale of investment percentage in DBP	$ 145	AUD 192
Percentage of access to be maintained in DBNGP transmission capacity for gas supply	30.00%	30.00%				20.00%
Exchange Traded Fixed Income and Equity Securities [Member]
Schedule of Equity Method Investments [Line Items]
Sales of investments			130
Loss on sale of investment			3
Loss on sale of investment, after tax			(2)
Carrying value of available-for-sale-securities			$ 83				$ 193