Common Stock, Shares, Option to Purchase Additional Shares

No definition available.

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- Definition

Common Stock, Shares, Sold

+ References

No definition available.

+ Details

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Data Type:	xbrli:sharesItemType
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Period Type:	instant

- Definition

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

+ References

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
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-Section 50
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

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Period Type:	duration

- Definition

Gross amount of debt extinguished.

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

Per share or per unit amount of equity securities issued.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of shares of stock issued during the period pursuant to acquisitions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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+ Details

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Period Type:	duration

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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SUBSEQUENT EVENTS SUBSEQUENT EVENTS (Details) - USD ($) $ / shares in Units, $ in Millions							3 Months Ended	12 Months Ended
	Mar. 12, 2021	Mar. 11, 2021	Dec. 09, 2020	Apr. 24, 2020	Mar. 27, 2020	Mar. 13, 2020	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Feb. 17, 2021	Feb. 11, 2021	Jun. 19, 2020	Apr. 17, 2020	Mar. 16, 2020
Subsequent Event [Line Items]
Common shares, issued (in shares)								506,832,537	301,886,794
Debt Instrument, Par Value								$ 5,595
Debt Extinguished				$ 736				1,513	$ 724	$ 227
Subsequent Event [Member]
Subsequent Event [Line Items]
Common shares, issued (in shares)												20,000,000
Common Stock, Shares, Option to Purchase Additional Shares												9,000,000
Arcelor Mittal [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Common Stock, Shares, Sold												40,000,000
AK Steel [Member]
Subsequent Event [Line Items]
Debt Instrument, Par Value								132
9.875% 2025 Senior Secured Notes \| Subsequent Event [Member]
Subsequent Event [Line Items]
Debt Extinguished		$ 334					$ 334
9.875% 2025 Senior Secured Notes \| Cleveland-Cliffs Inc. [Member]
Subsequent Event [Line Items]
Debt Instrument, Par Value				$ 555				$ 955						$ 400
9.875% 2025 Senior Secured Notes \| Cleveland-Cliffs Inc. [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Debt Instrument, Redemption Price, Percentage		109.875%
Debt Extinguished		$ 322
9.875% 2025 Senior Secured Notes \| Debt Instrument, Redemption, Period One, Upon Equity Issuance \| Cleveland-Cliffs Inc. [Member]
Subsequent Event [Line Items]
Debt Instrument, Redemption Price, Percentage								109.875%
5.875% 2027 Senior Notes
Subsequent Event [Line Items]
Debt Extinguished								$ 195
5.875% 2027 Senior Notes \| Cleveland-Cliffs Inc. [Member]
Subsequent Event [Line Items]
Debt Instrument, Par Value								$ 556	750
5.875% 2027 Senior Notes \| Debt Instrument, Redemption, Period One, Upon Equity Issuance \| Cleveland-Cliffs Inc. [Member]
Subsequent Event [Line Items]
Debt Instrument, Redemption Price, Percentage								105.875%
6.75% 2026 Senior Secured Notes \| Cleveland-Cliffs Inc. [Member]
Subsequent Event [Line Items]
Debt Instrument, Par Value						$ 725		$ 845					$ 120
6.75% 2026 Senior Secured Notes \| Debt Instrument, Redemption, Period One, Upon Equity Issuance \| Cleveland-Cliffs Inc. [Member]
Subsequent Event [Line Items]
Debt Instrument, Redemption Price, Percentage								106.75%
4.625% 2029 Senior Notes \| Cleveland-Cliffs Inc. [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Debt Instrument, Par Value											$ 500
4.875% 2031 Senior Notes \| Cleveland-Cliffs Inc. [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Debt Instrument, Par Value											$ 500
4.875% 2024 Senior Secured Notes
Subsequent Event [Line Items]
Debt Extinguished								$ 6
4.875% 2024 Senior Secured Notes \| Cleveland-Cliffs Inc. [Member]
Subsequent Event [Line Items]
Debt Instrument, Par Value								395	$ 400
4.875% 2024 Senior Secured Notes \| Cleveland-Cliffs Inc. [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Debt Instrument, Redemption Price, Percentage	102.438%
Debt Extinguished	$ 395
6.375% 2025 Senior Notes
Subsequent Event [Line Items]
Debt Extinguished								168
6.375% 2025 Senior Notes \| Cleveland-Cliffs Inc. [Member]
Subsequent Event [Line Items]
Debt Instrument, Par Value								64							$ 232
6.375% 2025 Senior Notes \| Cleveland-Cliffs Inc. [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Debt Instrument, Redemption Price, Percentage	103.188%
Debt Extinguished	$ 64
7.625% 2021 AK Senior Notes
Subsequent Event [Line Items]
Debt Extinguished					$ 9	364		373
7.625% 2021 AK Senior Notes \| AK Steel [Member]
Subsequent Event [Line Items]
Debt Instrument, Par Value								34
7.625% 2021 AK Senior Notes \| AK Steel [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%
Debt Extinguished	$ 34
7.50% 2023 AK Senior Notes [Member]
Subsequent Event [Line Items]
Debt Extinguished					$ 56	$ 311		367
7.50% 2023 AK Senior Notes [Member] \| AK Steel [Member]
Subsequent Event [Line Items]
Debt Instrument, Par Value								13
7.50% 2023 AK Senior Notes [Member] \| AK Steel [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Debt Instrument, Redemption Price, Percentage	101.875%
Debt Extinguished	$ 13
6.375% 2025 AK Senior Notes
Subsequent Event [Line Items]
Debt Extinguished								9
6.375% 2025 AK Senior Notes \| AK Steel [Member]
Subsequent Event [Line Items]
Debt Instrument, Par Value								$ 29
6.375% 2025 AK Senior Notes \| AK Steel [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Debt Instrument, Redemption Price, Percentage	103.188%
Debt Extinguished	$ 29
Common Stock [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Common stock, shares issued, price per share												$ 16.12
ArcelorMittal USA [Member] \| Common Stock [Member]
Subsequent Event [Line Items]
Stock Issued During Period, Shares, Acquisitions			78,186,671					78,000,000