Summary of Significant Accounting Policies (Policies)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 2013
Accounting Policies [Abstract]
Cash Equivalents	Cash Equivalents Cash equivalents included money market funds totaling $856 million and $615 million for EME and $99 million and $75 million for Midwest Generation at June 30, 2013 and December 31, 2012, respectively. The carrying value of cash equivalents equals the fair value as all investments have original maturities of less than three months.
New Accounting Guidance	New Accounting Guidance Accounting Guidance Adopted in 2013 Offsetting Assets and Liabilities In December 2011 and December 2012, the Financial Accounting Standards Board (FASB) issued accounting standards updates modifying the disclosure requirements about the nature of an entity's rights of offsetting assets and liabilities in the consolidated balance sheet under master netting agreements and related arrangements associated with financial and derivative instruments. The guidance requires increased disclosure of the gross and net recognized assets and liabilities, collateral positions, and narrative descriptions of setoff rights. EME and Midwest Generation adopted this guidance effective January 1, 2013. Presentation of Items Reclassified out of Accumulated Other Comprehensive Income In February 2013, the FASB issued an accounting standards update which requires disclosure related to items reclassified out of accumulated other comprehensive income (AOCI). The guidance requires entities to present separately, for each component of other comprehensive income (OCI), current period reclassifications and the remainder of the current-period OCI. In addition, for certain current period reclassifications, an entity is required to disclose the effect of the item reclassified out of AOCI on the respective line item of net income. EME adopted this guidance effective January 1, 2013. Accounting Guidance Not Yet Adopted Joint and Several Liabilities In February 2013, the FASB issued an accounting standard update which modifies the requirements for the recognition, measurement, and disclosure of obligations resulting from joint and several liability arrangements for which the total amount of the obligation is fixed at the reporting date. The guidance requires companies to measure these obligations as the sum of the amount the company has agreed with co-obligors to pay and any additional amount it expects to pay on behalf of one or more co-obligors. This guidance is effective for fiscal years beginning after December 31, 2013. EME and Midwest Generation do not expect this guidance to have a material impact on results of operations. Presentation of Unrecognized Tax Benefits In July 2013, the FASB issued an accounting standard update which clarifies that a liability for an unrecognized tax benefit should be presented as a reduction of a deferred tax asset when settlement of the liability with the taxing authority results in the reduction of a net operating loss or tax credit carryforward. The requirement to record a non-cash settlement in a net manner does not affect EME and Midwest Generation's analysis of the realization of deferred tax assets. This guidance is effective for fiscal years beginning after December 31, 2013. EME and Midwest Generation do not expect this guidance to have a material impact on results of operations.

- Definition

Disclosure of accounting policy for cash and cash equivalents with respect to unrestricted balances.

+ References+ Details

MIDWEST GENERATION LLC 10-Q