Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2012

Inventory consisted of the following:



	EME				Midwest Generation
	December 31,				December 31,
(in millions)	2012		2011		2012		2011
Coal, fuel oil and other raw materials	$	123	$	120	$	119	$	117
Spare parts, materials and supplies	52		49		46		42
Total inventory	$	175	$	169	$	165	$	159

Property, Plant and Equipment

Estimated useful lives for property, plant and equipment are as follows:



	EME	Midwest Generation
Power plant facilities	2.75 to 35 years	2.75 to 30 years
Leasehold improvements	Shorter of life of lease or estimated useful life	Shorter of life of lease or estimated useful life
Emission allowances	25 to 33.75 years	25 to 33.75 years
Equipment, furniture and fixtures	3 to 10 years	3 to 7 years
Plant and equipment under lease financing	not applicable	30 to 33.75 years

The remaining estimated useful life or lease term at December 31, 2012 for the Midwest Generation plants is as follows. Estimated useful lives of individual facilities could be impacted by decisions related to the installation of environmental remediation equipment. If environmental compliance equipment is not installed, the useful life may be shortened.



	Joliet Unit 6	6 years
	Joliet Units 7 and 8¹	18 years
	Powerton Station¹	21 years
	Will County Station	17 years


¹	Represents leased facilities. The leases may be renewed based on criteria outlined in their respective agreements.

- Definition

The entire disclosure for inventory. This may include, but is not limited to, the basis of stating inventory, the method of determining inventory cost, the major classes of inventory, and the nature of the cost elements included in inventory. If inventory is stated above cost, accrued net losses on firm purchase commitments for inventory and losses resulting from valuing inventory at the lower-of-cost-or-market may also be included. For LIFO inventory, may disclose the amount and basis for determining the excess of replacement or current cost over stated LIFO value and the effects of a LIFO quantities liquidation that impacts net income.

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- Definition

Tabular disclosure of the useful life and salvage value of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

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