Commitments and Contingencies	6 Months Ended
Jun. 30, 2013
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies (EME and Midwest Generation, except as noted) Lease Commitments Powerton and Joliet Sale Leaseback Covenants in the Powerton and Joliet Sale Leaseback documents include restrictions on the ability of EME and Midwest Generation to, among other things, incur debt, create liens on their property, merge or consolidate, sell assets, make investments, engage in transactions with affiliates, make distributions, make capital expenditures, enter into agreements restricting their ability to make distributions, engage in other lines of business, enter into swap agreements, or engage in transactions for any speculative purpose. The filing of the Chapter 11 Cases constitutes an event of default under the Powerton and Joliet Sale Leaseback and under instruments governing the Senior Lease Obligation Bonds issued to finance these leases. Prior to the filing of the Chapter 11 Cases, EME and Midwest Generation had entered into a forbearance agreement with the owner-lessors, the owner-lessors' equity owners, and the Certificate Holders. Under the terms of the forbearance agreement, Midwest Generation did not make the scheduled lease payment of $76 million on January 2, 2013, but on February 15, 2013, did pay the ratable portion of the rent due under the leases attributable to the period between December 17, 2012 and January 2, 2013 of $7 million. This forbearance agreement has expired. In June 2013, EME and Midwest Generation agreed, among other things, to make monthly rental payments of $3.75 million beginning in July 2013, in lieu of the scheduled $76 million lease payment due on July 2, 2013. In addition, the Bankruptcy Court approved the extension of the statutory deadline by which the Debtor Entities must assume or reject the Powerton and Joliet leases until September 30, 2013. Each lease sets forth a termination value payable upon certain circumstances, which generally declines over time. A default under the terms of the Powerton and Joliet leases could result in foreclosure and a loss by Midwest Generation of its lease interest in the plant. In addition, under certain circumstances, a default would trigger obligations under EME's guarantee of such leases. These events could have an adverse effect on EME's and Midwest Generation's results of operations and financial position. Operating Lease Commitments At June 30, 2013, Midwest Generation had future minimum operating lease payments totaling approximately $4 million, which consists of $2 million for the remainder of 2013, $1 million for 2014, and $1 million for 2015. Future minimum operating lease commitments decreased from December 31, 2012 primarily due to amended contracts and the rejection of executory contracts in connection with the Chapter 11 Cases. Other Commitments Fuel Supply Contracts At June 30, 2013, Midwest Generation had commitments to purchase coal from third-party suppliers at fixed prices, subject to adjustment clauses. These commitments under existing agreements are estimated to aggregate $312 million, which consists of: $162 million for the remainder of 2013 and $150 million for 2014. Midwest Generation has the right to reject these fuel supply contracts in connection with the Chapter 11 Cases. In July 2013, Midwest Generation entered into additional contractual agreements for the purchase of coal. These commitments are estimated to be $35 million for the remainder of 2013. Capital Commitments At June 30, 2013, Midwest Generation had firm commitments to spend approximately $4 million during the remainder of 2013 for capital expenditures. Other Contractual Obligations At June 30, 2013, Midwest Generation had contractual commitments for the purchase of materials used in the operation of environmental controls equipment. These commitments are estimated to aggregate $25 million, which consists of $8 million for the remainder of 2013 and $17 million for 2014. Guarantees and Indemnities EME and certain of its subsidiaries have various financial and performance guarantees and indemnity agreements which are issued in the normal course of business. The contracts discussed below include performance guarantees. Environmental Indemnities Related to the Midwest Generation Plants In connection with the acquisition of the Midwest Generation plants, EME and Midwest Generation agreed to indemnify Commonwealth Edison Company (Commonwealth Edison) with respect to specified environmental liabilities before and after December 15, 1999, the date of sale. The indemnification obligations are reduced by any insurance proceeds and tax benefits related to such indemnified claims and are subject to a requirement that Commonwealth Edison takes all reasonable steps to mitigate losses related to any such indemnification claim. Also, in connection with the Powerton and Joliet Sale Leaseback, EME agreed to indemnify the owner-lessors for specified environmental liabilities. These indemnities are not limited in term or amount. Due to the nature of the obligations under these indemnities, a maximum potential liability cannot be determined. Commonwealth Edison has advised EME that Commonwealth Edison believes it is entitled to indemnification for all liabilities, costs, and expenses that it may be required to bear as a result of the litigation discussed below under "—Contingencies—Midwest Generation New Source Review and Other Litigation," and one of the Powerton-Joliet owner-lessors has made a similar request for indemnification. Except as discussed below, EME and Midwest Generation have not recorded a liability related to these environmental indemnities. Midwest Generation entered into a supplemental agreement with Commonwealth Edison and Exelon Generation Company LLC on February 20, 2003 to resolve a dispute regarding interpretation of Midwest Generation's reimbursement obligation for asbestos claims under the environmental indemnities set forth in the Asset Sale Agreement. Under this supplemental agreement, Midwest Generation agreed to reimburse Commonwealth Edison and Exelon Generation for 50% of specific asbestos claims pending as of February 2003 and related expenses less recovery of insurance costs and agreed to a sharing arrangement for liabilities and expenses associated with future asbestos-related claims as specified in the agreement. The obligations under this agreement are not subject to a maximum liability. The supplemental agreement had an initial five-year term with an automatic renewal provision for subsequent one-year terms (subject to the right of either party to terminate); pursuant to the automatic renewal provision, the supplemental agreement has been extended until February 2014. There were approximately 260 cases for which Midwest Generation was potentially liable that had not been settled and dismissed at June 30, 2013. Midwest Generation had $53 million recorded in LSTC at June 30, 2013 related to this contractual indemnity. For discussion of LSTC, see Note 14—Restructuring Activities. Indemnities Related to the Homer City Plant (EME only) In connection with the 1999 acquisition of the Homer City plant from New York State Electric & Gas Corporation (NYSEG) and Pennsylvania Electric Company (Penelec) (the sellers), Homer City agreed to indemnify the sellers with respect to specified environmental liabilities before and after the date of sale. EME guaranteed this indemnity obligation of Homer City. In connection with Homer City's divestiture of assets to an affiliate of General Electric Capital Corporation (GECC) on December 14, 2012, EME re-affirmed its guaranty to NYSEG and Penelec. Also in connection with the recent asset transfer to the GECC affiliate, all operative documents with respect to Homer City's sale leaseback (including all EME indemnities in favor of the former owner-lessors) were terminated. In connection with the transfer, the GECC affiliate did not assume (and Homer City retained) liabilities for monetary fines and penalties for violations of environmental laws or environmental permits prior to the closing date. EME has not recorded a liability related to this indemnity. For discussion of the New Source Review lawsuit filed against Homer City, see "—Contingencies—Homer City New Source Review and Other Litigation." Indemnities Provided under Asset Sale and Sale Leaseback Agreements The asset sale agreements for the sale of EME's international assets contain indemnities from EME to the purchasers, including indemnification for taxes imposed with respect to operations of the assets prior to the sale and for pre-closing environmental liabilities. Not all indemnities under the asset sale agreements have specific expiration dates. At June 30, 2013, EME had $19 million recorded in LSTC related to these matters. For discussion of LSTC, see Note 14—Restructuring Activities. In connection with the Powerton and Joliet Sale Leaseback and, previously, a sale leaseback transaction related to the Collins Station in Illinois, EME, Midwest Generation, and another wholly owned subsidiary of EME entered into tax indemnity agreements. Under certain of these tax indemnity agreements, Midwest Generation, as the lessee in the Powerton and Joliet Sale Leaseback, agreed to indemnify the respective owner-lessors for specified adverse tax consequences that could result from certain situations set forth in each tax indemnity agreement, including specified defaults under the respective leases. Although the Collins Station lease terminated in April 2004, Midwest Generation's indemnities in favor of its former lease equity investors are still in effect. EME provided similar indemnities in the Powerton and Joliet Sale Leaseback. The potential indemnity obligations under these tax indemnity agreements could be significant. Due to the nature of these potential obligations, EME and Midwest Generation cannot determine a range of estimated obligations which would be triggered by a valid claim from the owner-lessors. EME and Midwest Generation have not recorded a liability for these matters. Other Indemnities EME and Midwest Generation provide other indemnifications through contracts entered into in the normal course of business. These include, among other things, indemnities for specified environmental liabilities and for income taxes with respect to assets sold. EME's and Midwest Generation's obligations under these agreements may or may not be limited in terms of time and/or amount, and in some instances, EME and Midwest Generation may have recourse against third parties. EME and Midwest Generation cannot determine a range of estimates and have not recorded a liability related to these indemnities. Contingencies In addition to the matters disclosed in these notes, EME and Midwest Generation are involved in other legal, tax, and regulatory proceedings before various courts and governmental agencies regarding matters arising in the ordinary course of business. EME and Midwest Generation believe the outcome of these other proceedings, individually and in the aggregate, will not materially affect their results of operations or liquidity. Midwest Generation New Source Review and Other Litigation In August 2009, the United States Environmental Protection Agency (US EPA) and the State of Illinois filed a complaint in the United States District Court for the Northern District of Illinois alleging that Midwest Generation or Commonwealth Edison performed repair or replacement projects at six Illinois coal-fired electric generating stations in violation of the Prevention of Significant Deterioration (PSD) requirements and of the New Source Performance Standards of the Clean Air Act (CAA), including alleged requirements to obtain a construction permit and to install controls sufficient to meet best available control technology (BACT) emission rates. The US EPA also alleged that Midwest Generation and Commonwealth Edison violated certain operating permit requirements under Title V of the CAA. Finally, the US EPA alleged violations of certain opacity and particulate matter standards at the Midwest Generation plants. In addition to seeking penalties ranging from $25,000 to $37,500 per violation per day, the complaint called for an injunction ordering Midwest Generation to install controls sufficient to meet BACT emission rates at all units subject to the complaint and other remedies. The remedies sought by the plaintiffs in the lawsuit could go well beyond the requirements of the Combined Pollutant Standard (CPS). Several Chicago-based environmental action groups intervened in the case. Nine of the ten PSD claims raised in the complaint have been dismissed, along with claims related to alleged violations of Title V of the CAA, to the extent based on the dismissed PSD claims, and all claims asserted against Commonwealth Edison and EME. The dismissals were affirmed by the Seventh Circuit Court of Appeals in July 2013. The court denied a motion to dismiss a claim by the Chicago-based environmental action groups for civil penalties in the remaining PSD claim but noted that the plaintiffs will be required to convince the court that the statute of limitations should be equitably tolled. The court did not address other counts in the complaint that allege violations of opacity and particulate matter limitations under the Illinois State Implementation Plan and Title V of the CAA. In February 2012, certain of the environmental action groups that had intervened in the case entered into an agreement with Midwest Generation to dismiss without prejudice all of their opacity claims as to all defendants. The agreed upon motion to dismiss was approved by the court on March 26, 2012. In January 2012, two complaints were filed against Midwest Generation in Illinois state court by residents living near the Crawford and Fisk Stations on behalf of themselves and all others similarly situated, each asserting claims of nuisance, negligence, trespass, and strict liability. The plaintiffs seek to have their suits certified as a class action and request injunctive relief, as well as compensatory and punitive damages. The complaints are similar to two complaints previously filed in the United States District Court for the Northern District of Illinois, which were dismissed in October 2011 for lack of federal jurisdiction. Midwest Generation's motions to dismiss the cases were denied in August 2012, following which the plaintiffs filed amended complaints alleging substantially similar claims and requesting similar relief. Midwest Generation has filed motions to dismiss the amended complaints, and these complaints are stayed as a result of the Chapter 11 Cases. In October 2012, Midwest Generation and the Illinois Environmental Protection Agency entered into Compliance Commitment Agreements outlining specified environmental remediation measures and groundwater monitoring activities to be undertaken at its Powerton, Joliet, Crawford, Will County, and Waukegan generating stations. Also in October 2012, several environmental groups filed a complaint before the Illinois Pollution Control Board against Midwest Generation, alleging violations of the Illinois groundwater standards through the operation of coal ash disposal ponds at its Powerton, Joliet, Waukegan, and Will County generating stations. The complaint requests the imposition of civil penalties, injunctive relief, and remediation. The matter is currently stayed as a result of the Chapter 11 Cases, although that stay was lifted in part in April 2013 so that the proceedings may continue for the sole purpose of adjudicating Midwest Generation's motion to dismiss the complaint. In December 2012, the Sierra Club filed a complaint before the Illinois Pollution Control Board against Midwest Generation, alleging violations of sulfur dioxide (SO₂) emissions standards at its Powerton, Joliet, Waukegan, and Will County generating stations. The complaint is based on alleged violations of the US EPA National Ambient Air Quality Standards (NAAQS) regulations for 1-hour SO₂, which have not yet been incorporated into any specific state implementation plan in Illinois. The complaint requests the imposition of civil penalties, injunctive relief, and the imposition of further reductions on SO₂emissions to offset past emissions. The complaint is now stayed as a result of the Chapter 11 Cases. Adverse decisions in these cases could involve penalties, remedial actions, and damages that could have a material impact on the financial condition and results of operations of Midwest Generation and EME. EME cannot predict the outcome of these matters or estimate the impact on the Midwest Generation plants, or EME's and Midwest Generation's results of operations, financial position, or cash flows. EME and Midwest Generation have not recorded a liability for these matters. Homer City New Source Review and Other Litigation (EME only) In January 2011, the US EPA filed a complaint in the United States District Court for the Western District of Pennsylvania against Homer City, the sale leaseback owner participants of the Homer City plant, and two prior owners of the Homer City plant. The complaint alleged violations of the PSD and Title V provisions of the CAA as a result of projects in the 1990s performed by prior owners without PSD permits and the subsequent failure to incorporate emissions limitations that meet BACT into the station's Title V operating permit. In addition to seeking penalties ranging from $32,500 to $37,500 per violation per day, the complaint called for an injunction ordering Homer City to install controls sufficient to meet BACT emission rates at all units subject to the complaint and for other remedies. The PADEP, the State of New York, and the State of New Jersey intervened in the lawsuit. In October 2011, all of the claims in the US EPA's lawsuit were dismissed with prejudice. An appeal of the dismissal is pending before the United States Court of Appeals for the Third Circuit. Also in January 2011, two residents filed a complaint in the United States District Court for the Western District of Pennsylvania, on behalf of themselves and all others similarly situated, against Homer City, the sale leaseback owner participants of the Homer City plant, two prior owners of the Homer City plant, EME, and EIX, claiming that emissions from the Homer City plant had adversely affected their health and property values. The plaintiffs sought to have their suit certified as a class action and requested injunctive relief, the funding of a health assessment study and medical monitoring, as well as compensatory and punitive damages. In October 2011, the claims in the purported class action lawsuit that were based on the federal CAA were dismissed with prejudice, while state law statutory and common law claims were dismissed without prejudice to re-file in state court should the plaintiffs choose to do so. EME does not know whether the plaintiffs will file a complaint in state court. Adverse decisions in these cases could involve penalties, remedial actions, and damages. EME cannot predict the outcome of these matters or estimate the impact on its results of operations, financial position, or cash flows. EME has not recorded a liability for these matters. Environmental Remediation Legislative and regulatory activities by federal, state, and local authorities in the United States relating to energy and the environment impose numerous restrictions and requirements with respect to the operation of EME's existing facilities, including the Midwest Generation plants, and affect the timing, cost, location, design, construction, and operation of new facilities by EME's subsidiaries, as well as the cost of mitigating the environmental impacts of past operations. With respect to potential liabilities arising under the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA) or similar laws for the investigation and remediation of contaminated property, EME and Midwest Generation accrue a liability to the extent the costs are probable and can be reasonably estimated. Midwest Generation had accrued a probable amount of approximately $8 million at June 30, 2013 for estimated environmental investigation and remediation costs for two stations at the Midwest Generation plants. This estimate is based upon the number of sites, the scope of work, and the estimated costs for investigation and/or remediation where such expenditures could be reasonably estimated. EME and Midwest Generation also have identified sites for which a reasonable estimate cannot be made. Future estimated costs may vary based on changes in regulations or requirements of federal, state or local governmental agencies, changes in technology, and actual costs of disposal. In addition, future remediation costs will be affected by the nature and extent of contamination discovered at the sites that require remediation. Given the prior history of the operations at its facilities, EME and Midwest Generation cannot be certain that the existence or extent of all contamination at its sites has been fully identified. Chevron Adversary Proceeding (EME only) In December 2012, Chevron Kern River Company and Chevron Sycamore Cogeneration Company filed a complaint against Southern Sierra Energy Company and Western Sierra Energy in the Chapter 11 Cases. The plaintiffs and defendants are partners in the Kern River and Sycamore projects. The complaint alleged that the filing of the Chapter 11 Cases constituted a default under the partnership agreements related to those projects, entitling the defendants to expel the plaintiffs from the partnerships and pay for their interests at a price based on the net book value of the partnerships, and sought a declaratory judgment, injunctive relief, and relief from the automatic stay in support of those alleged remedies. In January 2013, the Bankruptcy Court denied the plaintiffs' request for relief from the automatic stay and a preliminary injunction. The plaintiffs have filed a notice of appeal, and the defendants have moved to stay proceedings until the plaintiffs' appeal is decided. The Bankruptcy Court has twice continued the proceedings, and the next hearing is scheduled for August 21, 2013.

Commitments and Contingencies (EME and Midwest Generation, except as noted)

Lease Commitments

Powerton and Joliet Sale Leaseback

Covenants in the Powerton and Joliet Sale Leaseback documents include restrictions on the ability of EME and Midwest Generation to, among other things, incur debt, create liens on their property, merge or consolidate, sell assets, make investments, engage in transactions with affiliates, make distributions, make capital expenditures, enter into agreements restricting their ability to make distributions, engage in other lines of business, enter into swap agreements, or engage in transactions for any speculative purpose.

The filing of the Chapter 11 Cases constitutes an event of default under the Powerton and Joliet Sale Leaseback and under instruments governing the Senior Lease Obligation Bonds issued to finance these leases. Prior to the filing of the Chapter 11 Cases, EME and Midwest Generation had entered into a forbearance agreement with the owner-lessors, the owner-lessors' equity owners, and the Certificate Holders. Under the terms of the forbearance agreement, Midwest Generation did not make the scheduled lease payment of $76 million on January 2, 2013, but on February 15, 2013, did pay the ratable portion of the rent due under the leases attributable to the period between December 17, 2012 and January 2, 2013 of $7 million. This forbearance agreement has expired. In June 2013, EME and Midwest Generation agreed, among other things, to make monthly rental payments of $3.75 million beginning in July 2013, in lieu of the scheduled $76 million lease payment due on July 2, 2013. In addition, the Bankruptcy Court approved the extension of the statutory deadline by which the Debtor Entities must assume or reject the Powerton and Joliet leases until September 30, 2013.

Each lease sets forth a termination value payable upon certain circumstances, which generally declines over time. A default under the terms of the Powerton and Joliet leases could result in foreclosure and a loss by Midwest Generation of its lease interest in the plant. In addition, under certain circumstances, a default would trigger obligations under EME's guarantee of such leases. These events could have an adverse effect on EME's and Midwest Generation's results of operations and financial position.

Operating Lease Commitments

At June 30, 2013, Midwest Generation had future minimum operating lease payments totaling approximately $4 million, which consists of $2 million for the remainder of 2013, $1 million for 2014, and $1 million for 2015. Future minimum operating lease commitments decreased from December 31, 2012 primarily due to amended contracts and the rejection of executory contracts in connection with the Chapter 11 Cases.

Other Commitments

Fuel Supply Contracts

At June 30, 2013, Midwest Generation had commitments to purchase coal from third-party suppliers at fixed prices, subject to adjustment clauses. These commitments under existing agreements are estimated to aggregate $312 million, which consists of: $162 million for the remainder of 2013 and $150 million for 2014. Midwest Generation has the right to reject these fuel supply contracts in connection with the Chapter 11 Cases. In July 2013, Midwest Generation entered into additional contractual agreements for the purchase of coal. These commitments are estimated to be $35 million for the remainder of 2013.

Capital Commitments

At June 30, 2013, Midwest Generation had firm commitments to spend approximately $4 million during the remainder of 2013 for capital expenditures.

Other Contractual Obligations

At June 30, 2013, Midwest Generation had contractual commitments for the purchase of materials used in the operation of environmental controls equipment. These commitments are estimated to aggregate $25 million, which consists of $8 million for the remainder of 2013 and $17 million for 2014.

Guarantees and Indemnities

EME and certain of its subsidiaries have various financial and performance guarantees and indemnity agreements which are issued in the normal course of business. The contracts discussed below include performance guarantees.

Environmental Indemnities Related to the Midwest Generation Plants

In connection with the acquisition of the Midwest Generation plants, EME and Midwest Generation agreed to indemnify Commonwealth Edison Company (Commonwealth Edison) with respect to specified environmental liabilities before and after December 15, 1999, the date of sale. The indemnification obligations are reduced by any insurance proceeds and tax benefits related to such indemnified claims and are subject to a requirement that Commonwealth Edison takes all reasonable steps to mitigate losses related to any such indemnification claim. Also, in connection with the Powerton and Joliet Sale Leaseback, EME agreed to indemnify the owner-lessors for specified environmental liabilities. These indemnities are not limited in term or amount. Due to the nature of the obligations under these indemnities, a maximum potential liability cannot be determined. Commonwealth Edison has advised EME that Commonwealth Edison believes it is entitled to indemnification for all liabilities, costs, and expenses that it may be required to bear as a result of the litigation discussed below under "—Contingencies—Midwest Generation New Source Review and Other Litigation," and one of the Powerton-Joliet owner-lessors has made a similar request for indemnification. Except as discussed below, EME and Midwest Generation have not recorded a liability related to these environmental indemnities.

Midwest Generation entered into a supplemental agreement with Commonwealth Edison and Exelon Generation Company LLC on February 20, 2003 to resolve a dispute regarding interpretation of Midwest Generation's reimbursement obligation for asbestos claims under the environmental indemnities set forth in the Asset Sale Agreement. Under this supplemental agreement, Midwest Generation agreed to reimburse Commonwealth Edison and Exelon Generation for 50% of specific asbestos claims pending as of February 2003 and related expenses less recovery of insurance costs and agreed to a sharing arrangement for liabilities and expenses associated with future asbestos-related claims as specified in the agreement. The obligations under this agreement are not subject to a maximum liability. The supplemental agreement had an initial five-year term with an automatic renewal provision for subsequent one-year terms (subject to the right of either party to terminate); pursuant to the automatic renewal provision, the supplemental agreement has been extended until February 2014. There were approximately 260 cases for which Midwest Generation was potentially liable that had not been settled and dismissed at June 30, 2013. Midwest Generation had $53 million recorded in LSTC at June 30, 2013 related to this contractual indemnity. For discussion of LSTC, see Note 14—Restructuring Activities.

Indemnities Related to the Homer City Plant (EME only)

In connection with the 1999 acquisition of the Homer City plant from New York State Electric & Gas Corporation (NYSEG) and Pennsylvania Electric Company (Penelec) (the sellers), Homer City agreed to indemnify the sellers with respect to specified environmental liabilities before and after the date of sale. EME guaranteed this indemnity obligation of Homer City. In connection with Homer City's divestiture of assets to an affiliate of General Electric Capital Corporation (GECC) on December 14, 2012, EME re-affirmed its guaranty to NYSEG and Penelec. Also in connection with the recent asset transfer to the GECC affiliate, all operative documents with respect to Homer City's sale leaseback (including all EME indemnities in favor of the former owner-lessors) were terminated. In connection with the transfer, the GECC affiliate did not assume (and Homer City retained) liabilities for monetary fines and penalties for violations of environmental laws or environmental permits prior to the closing date. EME has not recorded a liability related to this indemnity. For discussion of the New Source Review lawsuit filed against Homer City, see "—Contingencies—Homer City New Source Review and Other Litigation."

Indemnities Provided under Asset Sale and Sale Leaseback Agreements

The asset sale agreements for the sale of EME's international assets contain indemnities from EME to the purchasers, including indemnification for taxes imposed with respect to operations of the assets prior to the sale and for pre-closing environmental liabilities. Not all indemnities under the asset sale agreements have specific expiration dates. At June 30, 2013, EME had $19 million recorded in LSTC related to these matters. For discussion of LSTC, see Note 14—Restructuring Activities.

In connection with the Powerton and Joliet Sale Leaseback and, previously, a sale leaseback transaction related to the Collins Station in Illinois, EME, Midwest Generation, and another wholly owned subsidiary of EME entered into tax indemnity agreements. Under certain of these tax indemnity agreements, Midwest Generation, as the lessee in the Powerton and Joliet Sale Leaseback, agreed to indemnify the respective owner-lessors for specified adverse tax consequences that could result from certain situations set forth in each tax indemnity agreement, including specified defaults under the respective leases. Although the Collins Station lease terminated in April 2004, Midwest Generation's indemnities in favor of its former lease equity investors are still in effect. EME provided similar indemnities in the Powerton and Joliet Sale Leaseback. The potential indemnity obligations under these tax indemnity agreements could be significant. Due to the nature of these potential obligations, EME and Midwest Generation cannot determine a range of estimated obligations which would be triggered by a valid claim from the owner-lessors. EME and Midwest Generation have not recorded a liability for these matters.

Other Indemnities

EME and Midwest Generation provide other indemnifications through contracts entered into in the normal course of business. These include, among other things, indemnities for specified environmental liabilities and for income taxes with respect to assets sold. EME's and Midwest Generation's obligations under these agreements may or may not be limited in terms of time and/or amount, and in some instances, EME and Midwest Generation may have recourse against third parties. EME and Midwest Generation cannot determine a range of estimates and have not recorded a liability related to these indemnities.

Contingencies

In addition to the matters disclosed in these notes, EME and Midwest Generation are involved in other legal, tax, and regulatory proceedings before various courts and governmental agencies regarding matters arising in the ordinary course of business. EME and Midwest Generation believe the outcome of these other proceedings, individually and in the aggregate, will not materially affect their results of operations or liquidity.

Midwest Generation New Source Review and Other Litigation

In August 2009, the United States Environmental Protection Agency (US EPA) and the State of Illinois filed a complaint in the United States District Court for the Northern District of Illinois alleging that Midwest Generation or Commonwealth Edison performed repair or replacement projects at six Illinois coal-fired electric generating stations in violation of the Prevention of Significant Deterioration (PSD) requirements and of the New Source Performance Standards of the Clean Air Act (CAA), including alleged requirements to obtain a construction permit and to install controls sufficient to meet best available control technology (BACT) emission rates. The US EPA also alleged that Midwest Generation and Commonwealth Edison violated certain operating permit requirements under Title V of the CAA. Finally, the US EPA alleged violations of certain opacity and particulate matter standards at the Midwest Generation plants. In addition to seeking penalties ranging from $25,000 to $37,500 per violation per day, the complaint called for an injunction ordering Midwest Generation to install controls sufficient to meet BACT emission rates at all units subject to the complaint and other remedies. The remedies sought by the plaintiffs in the lawsuit could go well beyond the requirements of the Combined Pollutant Standard (CPS). Several Chicago-based environmental action groups intervened in the case.

Nine of the ten PSD claims raised in the complaint have been dismissed, along with claims related to alleged violations of Title V of the CAA, to the extent based on the dismissed PSD claims, and all claims asserted against Commonwealth Edison and EME. The dismissals were affirmed by the Seventh Circuit Court of Appeals in July 2013. The court denied a motion to dismiss a claim by the Chicago-based environmental action groups for civil penalties in the remaining PSD claim but noted that the plaintiffs will be required to convince the court that the statute of limitations should be equitably tolled. The court did not address other counts in the complaint that allege violations of opacity and particulate matter limitations under the Illinois State Implementation Plan and Title V of the CAA. In February 2012, certain of the environmental action groups that had intervened in the case entered into an agreement with Midwest Generation to dismiss without prejudice all of their opacity claims as to all defendants. The agreed upon motion to dismiss was approved by the court on March 26, 2012.

In January 2012, two complaints were filed against Midwest Generation in Illinois state court by residents living near the Crawford and Fisk Stations on behalf of themselves and all others similarly situated, each asserting claims of nuisance, negligence, trespass, and strict liability. The plaintiffs seek to have their suits certified as a class action and request injunctive relief, as well as compensatory and punitive damages. The complaints are similar to two complaints previously filed in the United States District Court for the Northern District of Illinois, which were dismissed in October 2011 for lack of federal jurisdiction. Midwest Generation's motions to dismiss the cases were denied in August 2012, following which the plaintiffs filed amended complaints alleging substantially similar claims and requesting similar relief. Midwest Generation has filed motions to dismiss the amended complaints, and these complaints are stayed as a result of the Chapter 11 Cases.

In October 2012, Midwest Generation and the Illinois Environmental Protection Agency entered into Compliance Commitment Agreements outlining specified environmental remediation measures and groundwater monitoring activities to be undertaken at its Powerton, Joliet, Crawford, Will County, and Waukegan generating stations. Also in October 2012, several environmental groups filed a complaint before the Illinois Pollution Control Board against Midwest Generation, alleging violations of the Illinois groundwater standards through the operation of coal ash disposal ponds at its Powerton, Joliet, Waukegan, and Will County generating stations. The complaint requests the imposition of civil penalties, injunctive relief, and remediation. The matter is currently stayed as a result of the Chapter 11 Cases, although that stay was lifted in part in April 2013 so that the proceedings may continue for the sole purpose of adjudicating Midwest Generation's motion to dismiss the complaint.

In December 2012, the Sierra Club filed a complaint before the Illinois Pollution Control Board against Midwest Generation, alleging violations of sulfur dioxide (SO₂) emissions standards at its Powerton, Joliet, Waukegan, and Will County generating stations. The complaint is based on alleged violations of the US EPA National Ambient Air Quality Standards (NAAQS) regulations for 1-hour SO₂, which have not yet been incorporated into any specific state implementation plan in Illinois. The complaint requests the imposition of civil penalties, injunctive relief, and the imposition of further reductions on SO₂emissions to offset past emissions. The complaint is now stayed as a result of the Chapter 11 Cases.

Adverse decisions in these cases could involve penalties, remedial actions, and damages that could have a material impact on the financial condition and results of operations of Midwest Generation and EME. EME cannot predict the outcome of these matters or estimate the impact on the Midwest Generation plants, or EME's and Midwest Generation's results of operations, financial position, or cash flows. EME and Midwest Generation have not recorded a liability for these matters.

Homer City New Source Review and Other Litigation (EME only)

In January 2011, the US EPA filed a complaint in the United States District Court for the Western District of Pennsylvania against Homer City, the sale leaseback owner participants of the Homer City plant, and two prior owners of the Homer City plant. The complaint alleged violations of the PSD and Title V provisions of the CAA as a result of projects in the 1990s performed by prior owners without PSD permits and the subsequent failure to incorporate emissions limitations that meet BACT into the station's Title V operating permit. In addition to seeking penalties ranging from $32,500 to $37,500 per violation per day, the complaint called for an injunction ordering Homer City to install controls sufficient to meet BACT emission rates at all units subject to the complaint and for other remedies. The PADEP, the State of New York, and the State of New Jersey intervened in the lawsuit. In October 2011, all of the claims in the US EPA's lawsuit were dismissed with prejudice. An appeal of the dismissal is pending before the United States Court of Appeals for the Third Circuit.

Also in January 2011, two residents filed a complaint in the United States District Court for the Western District of Pennsylvania, on behalf of themselves and all others similarly situated, against Homer City, the sale leaseback owner participants of the Homer City plant, two prior owners of the Homer City plant, EME, and EIX, claiming that emissions from the Homer City plant had adversely affected their health and property values. The plaintiffs sought to have their suit certified as a class action and requested injunctive relief, the funding of a health assessment study and medical monitoring, as well as compensatory and punitive damages. In October 2011, the claims in the purported class action lawsuit that were based on the federal CAA were dismissed with prejudice, while state law statutory and common law claims were dismissed without prejudice to re-file in state court should the plaintiffs choose to do so. EME does not know whether the plaintiffs will file a complaint in state court.

Adverse decisions in these cases could involve penalties, remedial actions, and damages. EME cannot predict the outcome of these matters or estimate the impact on its results of operations, financial position, or cash flows. EME has not recorded a liability for these matters.

Environmental Remediation

Legislative and regulatory activities by federal, state, and local authorities in the United States relating to energy and the environment impose numerous restrictions and requirements with respect to the operation of EME's existing facilities, including the Midwest Generation plants, and affect the timing, cost, location, design, construction, and operation of new facilities by EME's subsidiaries, as well as the cost of mitigating the environmental impacts of past operations.

With respect to potential liabilities arising under the Comprehensive Environmental Response, Compensation and Liability Act of 1980 (CERCLA) or similar laws for the investigation and remediation of contaminated property, EME and Midwest Generation accrue a liability to the extent the costs are probable and can be reasonably estimated. Midwest Generation had accrued a probable amount of approximately $8 million at June 30, 2013 for estimated environmental investigation and remediation costs for two stations at the Midwest Generation plants. This estimate is based upon the number of sites, the scope of work, and the estimated costs for investigation and/or remediation where such expenditures could be reasonably estimated. EME and Midwest Generation also have identified sites for which a reasonable estimate cannot be made. Future estimated costs may vary based on changes in regulations or requirements of federal, state or local governmental agencies, changes in technology, and actual costs of disposal. In addition, future remediation costs will be affected by the nature and extent of contamination discovered at the sites that require remediation. Given the prior history of the operations at its facilities, EME and Midwest Generation cannot be certain that the existence or extent of all contamination at its sites has been fully identified.

Chevron Adversary Proceeding (EME only)

In December 2012, Chevron Kern River Company and Chevron Sycamore Cogeneration Company filed a complaint against Southern Sierra Energy Company and Western Sierra Energy in the Chapter 11 Cases. The plaintiffs and defendants are partners in the Kern River and Sycamore projects. The complaint alleged that the filing of the Chapter 11 Cases constituted a default under the partnership agreements related to those projects, entitling the defendants to expel the plaintiffs from the partnerships and pay for their interests at a price based on the net book value of the partnerships, and sought a declaratory judgment, injunctive relief, and relief from the automatic stay in support of those alleged remedies. In January 2013, the Bankruptcy Court denied the plaintiffs' request for relief from the automatic stay and a preliminary injunction. The plaintiffs have filed a notice of appeal, and the defendants have moved to stay proceedings until the plaintiffs' appeal is decided. The Bankruptcy Court has twice continued the proceedings, and the next hearing is scheduled for August 21, 2013.