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Carrying amount of all investments in debt and equity securities categorized as available-for-sale securities, reported at fair value. Includes restricted cash and investments primarily related to (a) funds held in trust for nuclear decommissioning and (b) debt service requirements that are restricted by certain project debt agreements to be used only for the related project. Includes equity method investments. Includes Rabbi trusts that hold corporate-owned life insurance on certain key executives and directors and represents the cash surrender value, net of any amounts borrowed against the cash surrender value.

No definition available.

Name:	mehc_InvestmentsIncludingEquityMethodAndRestrictedCashAndInvestments
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Carrying amount of investments in debt and equity securities categorized as available-for-sale securities, reported at fair value and expected to be used in operations within one year or the normal operating cycle, if longer. Includes restricted cash and investments primarily related to (a) funds held in trust for nuclear decommissioning and (b) debt service requirements that are restricted by certain project debt agreements to be used only for the related project. Includes equity method investments. Includes Rabbi trusts that hold corporate-owned life insurance on certain key executives and directors and represents the cash surrender value, net of any amounts borrowed against the cash surrender value.

No definition available.

Name:	mehc_InvestmentsIncludingEquityMethodAndRestrictedCashAndInvestmentsCurrent
Namespace Prefix:	mehc_
Data Type:	xbrli:monetaryItemType
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Carrying amount of investments in debt and equity securities categorized as available-for-sale securities, reported at fair value and not expected to be used in operations within one year or the normal operating cycle, if longer. Includes restricted cash and investments primarily related to (a) funds held in trust for nuclear decommissioning and (b) debt service requirements that are restricted by certain project debt agreements to be used only for the related project. Includes equity method investments. Includes Rabbi trusts that hold corporate-owned life insurance on certain key executives and directors and represents the cash surrender value, net of any amounts borrowed against the cash surrender value.

No definition available.

Name:	mehc_InvestmentsIncludingEquityMethodAndRestrictedCashAndInvestmentsNoncurrent
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The amount of investment tax credits netted against the equity method investment.

No definition available.

Name:	mehc_InvestmentTaxCreditIncludedInEquityMethodInvestment
Namespace Prefix:	mehc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of equity securities categorized neither as held-to-maturity nor as trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 320

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62557-112803

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (d)

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The fair value of investments held in a trust fund to pay for the costs of decontaminating and decommissioning facilities, whether such amount is presented as a separate caption or as a parenthetical disclosure on the balance sheet. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

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Balance Type:	debit
Period Type:	instant

- Details

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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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Sum of the carrying amounts as of the balance sheet date of all investments.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(h))

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-Name Regulation S-X (SX)

-Number 210

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This item represents the amount that could be realized under a life insurance contract or contracts owned by the Entity as of the date of the statement of financial position. Such Entity-owned life insurance policies are commonly known as corporate-owned life insurance (COLI) or bank-owned life insurance (BOLI).

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.12)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 12

-Article 5

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 325

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-URI http://asc.fasb.org/extlink&oid=6384206&loc=d3e41899-111602

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Other investments not otherwise specified in the taxonomy.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

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-Subparagraph (SX 210.5-02.12)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 12

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph g

-Article 7

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(f,g))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910