Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

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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- Definition

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

+ References

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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- Definition

Derivative, Extended Period

+ References

No definition available.

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- Definition

Financial Instruments and Commodity Contracts.

+ References

No definition available.

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- Definition

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994

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- Definition

Amount of the hedged item as of the balance sheet date related to the derivative. For example, the hedged balance on a debt instrument.

+ References

No definition available.

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- Definition

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

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- Definition

High end period remaining until maturity for the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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Financial Instruments and Commodity Contracts (Details Textual) Mg in Thousands, MMBTU in Millions, $ in Millions, ₩ in Billions	12 Months Ended
	Mar. 31, 2017 USD ($) Mg MMBTU	Mar. 31, 2017 KRW (₩) Mg MMBTU	Mar. 31, 2016 USD ($) Mg MMBTU	Mar. 31, 2016 KRW (₩) Mg MMBTU
Financial Instruments And Commodity Contracts [Abstract]
Derivative asset (liability)	$ (49)		$ 2
Expected reclassification of gains (losses) from AOCI to earnings	(43)
Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Derivative asset (liability)	(54)		14
Not Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Derivative asset (liability)	$ 5		$ (12)
Aluminum Forward Sales Contracts [Member] \| Not Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Higher remaining maturity range	1 year
Aluminium Contracts [Member]
Financial Instruments And Commodity Contracts [Abstract]
Notional amount (in tons) \| Mg	480	480	376	376
Aluminium Contracts [Member] \| Not Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Notional amount (in tons) \| Mg	89	89	76	76
Derivative asset (liability)	$ (11)		$ (2)
Currency Exchange Contracts [Member] \| Not Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Notional amount	683		636
Derivative asset (liability)	16		(1)
Electricity Swaps [Member] \| Not Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Derivative asset (liability)			$ (9)
Extended Electricity Swaps [Member] \| Not Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Notional amount	1
Derivative asset (liability)	$ 9
Derivative extended period	5 years
Natural Gas Swaps [Member]
Financial Instruments And Commodity Contracts [Abstract]
Higher remaining maturity range	1 year
Natural Gas Swaps [Member] \| Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Notional amount (in tons) \| MMBTU	6	6	5	5
Derivative asset (liability)	$ (1)		$ (4)
Natural Gas Swaps [Member] \| Not Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Notional amount (in tons) \| MMBTU	1	1
Derivative asset (liability)	$ (1)		$ (1)
Fuel [Member]
Financial Instruments And Commodity Contracts [Abstract]
Higher remaining maturity range	1 year
Fuel [Member] \| Not Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Notional amount (in tons) \| MMBTU	8	8
Derivative asset (liability)	$ (1)
Fair Value Hedging [Member] \| Forward Contracts [Member] \| Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Notional amount (in tons) \| Mg			1	1
Cash Flow Hedges [Member] \| Forward Contracts [Member] \| Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Notional amount (in tons) \| Mg	0	0	1	1
Cash Flow Hedges [Member] \| Aluminum Forward Sales Contracts [Member] \| Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Higher remaining maturity range	2 years
Notional amount (in tons) \| Mg	391	391	301	301
Cash Flow Hedges [Member] \| Aluminium Contracts [Member] \| Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Derivative asset (liability)	$ (69)		$ 8
Cash Flow Hedges [Member] \| Currency Exchange Contracts [Member]
Financial Instruments And Commodity Contracts [Abstract]
Notional amount	465		601
Cash Flow Hedges [Member] \| Currency Exchange Contracts [Member] \| Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Derivative asset (liability)	23		12
Cash Flow Hedges [Member] \| Interest Rate Swaps [Member] \| Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Derivative asset (liability)			(1)
Net Investment Hedging [Member] \| Currency Exchange Contracts [Member]
Financial Instruments And Commodity Contracts [Abstract]
Notional amount			36
Net Investment Hedging [Member] \| Currency Exchange Contracts [Member] \| Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Derivative asset (liability)			(1)
Long-term Debt [Member] \| Interest Rate Swaps [Member] \| Designated as Hedging Instrument [Member]
Financial Instruments And Commodity Contracts [Abstract]
Notional amount	119	₩ 133	$ 115	₩ 133
Interest rate swaps, hedged amount	$ 119	₩ 133
Derivative, fixed interest rate	2.92%	2.92%