Subsequent Events - Acquisitions	12 Months Ended
Dec. 31, 2011
Subsequent Events - Acquisitions [Abstract]
Subsequent Events [Text Block]	(23) Subsequent Events — Acquisitions In January 2012, MEHC, through a wholly-owned subsidiary, acquired Topaz Solar Farms LLC ("Topaz") and its 550-MW solar project (the "Topaz Project") in California from a subsidiary of First Solar, Inc. ("First Solar"). The Topaz Project is expected to cost approximately $2.44 billion, including all interest during construction, and will be completed in 22 blocks with an aggregate tested capacity of 586 MW. The Topaz Project expects to place 45 MW in service in 2012, 236 MW in service in 2013, 252 MW in service in 2014 and 53 MW in service in 2015. The Topaz Project is being constructed pursuant to a fixed price, date certain, turn-key engineering, procurement and construction contract with a subsidiary of First Solar. Topaz will sell all the electricity, renewable energy credits and other environmental attributes produced by the project to Pacific Gas and Electric Company ("PG&E") pursuant to a 25 year power purchase agreement. A subsidiary of First Solar will operate and maintain the project under a 25 year, fixed-fee operating and maintenance agreement. MEHC has committed to provide Topaz with equity to fund the costs of the Topaz Project in an amount up to $2.44 billion less, among other things, the gross proceeds of long-term debt issuances, project revenue prior to completion and the total equity contributions made by MEHC or its subsidiaries. If MEHC does not maintain a minimum credit rating from two of the following three ratings agencies of at least BBB- from Standard & Poor's Ratings Services or Fitch Ratings or Baa3 from Moody's Investors Service, MEHC's obligations under the equity commitment agreement would be supported by cash collateral or a letter of credit issued by a financial institution that meets certain minimum criteria specified in the financing documents. Upon reaching the final commercial operation date of the Topaz Project, MEHC will have no further obligation to make any equity contribution and any unused equity contribution obligations will be canceled. In February 2012, Topaz issued $850 million of the 5.75% Series A Senior Secured Notes. The principal of the notes amortize beginning September 2015 with a final maturity in September 2039. The net proceeds will be used to fund or reimburse the costs and expenses related to the development, construction and financing of the Topaz Project, including amounts that have been advanced by, or will be advanced by, MEHC for the Topaz Project. Any unused amounts will be invested or, in certain circumstances, loaned to MEHC. In connection with the offering, Topaz entered into a letter of credit and reimbursement facility in an aggregate principal amount of $345 million. Letters of credit issued under the letter of credit facility will be used to (a) provide security under the power purchase agreement and large generator interconnection agreements, (b) fund the debt service reserve requirement and the operation and maintenance debt service reserve requirement, (c) provide security for our remediation and mitigation liabilities, and (d) provide security in respect of our conditional use permit sales tax obligations. In January 2012, MEHC, through a wholly-owned subsidiary, acquired from NRG Energy, Inc. a 49 percent equity interest in Agua Caliente Solar, LLC ("Agua Caliente"), the owner of a 290-MW solar project (the "Agua Caliente Project") in Arizona. The Agua Caliente Project is expected to cost approximately $1.8 billion and will be completed in 12 blocks with an aggregate tested capacity of 310 MW. The first 30-MW block of the Agua Caliente Project was placed in service in January 2012 and the Agua Caliente Project expects to place 112 additional MW in service in 2012, 136 MW in service in 2013 and 32 MW in service in 2014. The project is being constructed pursuant to a fixed price, date certain, turn-key engineering, procurement and construction contract with a subsidiary of First Solar. Agua Caliente will sell all the electricity, renewable energy credits and other environmental attributes produced by the project to PG&E pursuant to a 25 year power purchase agreement. A subsidiary of First Solar will operate and maintain the project under a 25 year, fixed-fee operating and maintenance agreement. Construction costs are expected to be funded with equity contributions from MEHC and NRG Energy, Inc. and proceeds from a $967 million secured loan maturing in 2037 from an agency of the United States government as part of the United States Department of Energy loan guarantee program. Funding requests are submitted on a monthly basis and the approved loans accrue interest at a fixed rate based on the current average yield of comparable maturity United States Treasury rates plus a spread of 0.375%. Pursuant to an equity funding and contribution agreement, MEHC has committed to provide Agua Caliente with funding for (a) base equity contributions of up to an aggregative amount of $303 million for the construction of the project, and (b) transmission upgrade costs. In January 2012, MEHC entered into a $303 million letter of credit facility related to its funding commitments. The equity funding and contribution agreement and the letter of credit commitment decreases as equity is contributed to the Agua Caliente Project.

(23) Subsequent Events — Acquisitions

In January 2012, MEHC, through a wholly-owned subsidiary, acquired Topaz Solar Farms LLC ("Topaz") and its 550-MW solar project (the "Topaz Project") in California from a subsidiary of First Solar, Inc. ("First Solar"). The Topaz Project is expected to cost approximately $2.44 billion, including all interest during construction, and will be completed in 22 blocks with an aggregate tested capacity of 586 MW. The Topaz Project expects to place 45 MW in service in 2012, 236 MW in service in 2013, 252 MW in service in 2014 and 53 MW in service in 2015. The Topaz Project is being constructed pursuant to a fixed price, date certain, turn-key engineering, procurement and construction contract with a subsidiary of First Solar. Topaz will sell all the electricity, renewable energy credits and other environmental attributes produced by the project to Pacific Gas and Electric Company ("PG&E") pursuant to a 25 year power purchase agreement. A subsidiary of First Solar will operate and maintain the project under a 25 year, fixed-fee operating and maintenance agreement.

MEHC has committed to provide Topaz with equity to fund the costs of the Topaz Project in an amount up to $2.44 billion less, among other things, the gross proceeds of long-term debt issuances, project revenue prior to completion and the total equity contributions made by MEHC or its subsidiaries. If MEHC does not maintain a minimum credit rating from two of the following three ratings agencies of at least BBB- from Standard & Poor's Ratings Services or Fitch Ratings or Baa3 from Moody's Investors Service, MEHC's obligations under the equity commitment agreement would be supported by cash collateral or a letter of credit issued by a financial institution that meets certain minimum criteria specified in the financing documents. Upon reaching the final commercial operation date of the Topaz Project, MEHC will have no further obligation to make any equity contribution and any unused equity contribution obligations will be canceled.

In February 2012, Topaz issued $850 million of the 5.75% Series A Senior Secured Notes. The principal of the notes amortize beginning September 2015 with a final maturity in September 2039. The net proceeds will be used to fund or reimburse the costs and expenses related to the development, construction and financing of the Topaz Project, including amounts that have been advanced by, or will be advanced by, MEHC for the Topaz Project. Any unused amounts will be invested or, in certain circumstances, loaned to MEHC.

In connection with the offering, Topaz entered into a letter of credit and reimbursement facility in an aggregate principal amount of $345 million. Letters of credit issued under the letter of credit facility will be used to (a) provide security under the power purchase agreement and large generator interconnection agreements, (b) fund the debt service reserve requirement and the operation and maintenance debt service reserve requirement, (c) provide security for our remediation and mitigation liabilities, and (d) provide security in respect of our conditional use permit sales tax obligations.

In January 2012, MEHC, through a wholly-owned subsidiary, acquired from NRG Energy, Inc. a 49 percent equity interest in Agua Caliente Solar, LLC ("Agua Caliente"), the owner of a 290-MW solar project (the "Agua Caliente Project") in Arizona. The Agua Caliente Project is expected to cost approximately $1.8 billion and will be completed in 12 blocks with an aggregate tested capacity of 310 MW. The first 30-MW block of the Agua Caliente Project was placed in service in January 2012 and the Agua Caliente Project expects to place 112 additional MW in service in 2012, 136 MW in service in 2013 and 32 MW in service in 2014. The project is being constructed pursuant to a fixed price, date certain, turn-key engineering, procurement and construction contract with a subsidiary of First Solar. Agua Caliente will sell all the electricity, renewable energy credits and other environmental attributes produced by the project to PG&E pursuant to a 25 year power purchase agreement. A subsidiary of First Solar will operate and maintain the project under a 25 year, fixed-fee operating and maintenance agreement. Construction costs are expected to be funded with equity contributions from MEHC and NRG Energy, Inc. and proceeds from a $967 million secured loan maturing in 2037 from an agency of the United States government as part of the United States Department of Energy loan guarantee program. Funding requests are submitted on a monthly basis and the approved loans accrue interest at a fixed rate based on the current average yield of comparable maturity United States Treasury rates plus a spread of 0.375%.

Pursuant to an equity funding and contribution agreement, MEHC has committed to provide Agua Caliente with funding for (a) base equity contributions of up to an aggregative amount of $303 million for the construction of the project, and (b) transmission upgrade costs. In January 2012, MEHC entered into a $303 million letter of credit facility related to its funding commitments. The equity funding and contribution agreement and the letter of credit commitment decreases as equity is contributed to the Agua Caliente Project.