- Definition

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

+ 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

+ Details

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Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- 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

+ Details

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Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

When an investment contract or contracts have a range of settlement dates, the latest settlement date.

+ 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

+ Details

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Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

When an investment contract or contracts have a range of settlement dates, the earliest settlement date.

+ 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

+ Details

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Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- 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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Period Type:	duration

- Details

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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	aks_DerivativeCommodityContractByCommodityAxis=aks_NaturalGasMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	aks_DerivativeCommodityContractByCommodityAxis=aks_ZincMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Data Type:	na
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- Details

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- Details

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Derivative Instruments and Hedging Activities (Details)	12 Months Ended
Derivative Instruments and Hedging Activities (Details)	Dec. 31, 2018 CAD ($) MMBTU MW t lb	Dec. 31, 2018 EUR (€) MMBTU MW t lb	Dec. 31, 2017 CAD ($) MMBTU MW t lb	Dec. 31, 2017 EUR (€) MMBTU MW t lb
Commodity Contract [Member] \| Nickel [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives	0	0	500,000	500,000
Commodity Contract [Member] \| Natural Gas [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives \| MMBTU	39,868,000	39,868,000	41,338,000	41,338,000
Investment Contract Settlement Date Range Start	Jan. 01, 2019
Investment Contract Settlement Date Range End	Dec. 31, 2020
Commodity Contract [Member] \| Zinc [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives	52,150,000	52,150,000	50,350,000	50,350,000
Investment Contract Settlement Date Range Start	Jan. 01, 2019
Investment Contract Settlement Date Range End	Dec. 31, 2020
Commodity Contract [Member] \| Iron Ore [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives \| t	2,125,000	2,125,000	2,340,000	2,340,000
Investment Contract Settlement Date Range Start	Jan. 01, 2019
Investment Contract Settlement Date Range End	Dec. 31, 2020
Commodity Contract [Member] \| Electricity [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives \| MW	1,461,000	1,461,000	1,553,000	1,553,000
Investment Contract Settlement Date Range Start	Jan. 01, 2019
Investment Contract Settlement Date Range End	Sep. 30, 2020
Foreign Exchange Contract [Member] \| Euro Member Countries, Euro
Derivative [Line Items]
Derivative, Notional Amount \| €		€ 4,000,000		€ 26,000,000
Investment Contract Settlement Date Range Start	Jan. 01, 2019
Investment Contract Settlement Date Range End	Jun. 01, 2019
Foreign Exchange Contract [Member] \| Canada, Dollars
Derivative [Line Items]
Derivative, Notional Amount \| $	$ 118,560,000		$ 148,080,000
Investment Contract Settlement Date Range Start	Jan. 01, 2019
Investment Contract Settlement Date Range End	Dec. 31, 2021