Summary of Significant Accounting Policies (Policy)

6 Months Ended

Jun. 30, 2011

Summary of Significant Accounting Policies

General

On October 1, 2010, Ameren, CIPS, CILCO, IP, AERG and Resources Company completed a two-step corporate internal reorganization. The first step of the reorganization was the Ameren Illinois Merger. Upon consummation of the Ameren Illinois Merger, the separate legal existence of CILCO and IP terminated. The second step of the reorganization involved the distribution of AERG stock from Ameren Illinois to Ameren and the subsequent contribution by Ameren of the AERG stock to Resources Company. The Ameren Illinois Merger and the distribution of AERG stock were accounted for as transactions between entities under common control. In accordance with authoritative accounting guidance, assets and liabilities transferred between entities under common control were accounted for at the historical cost basis of the common parent, Ameren, as if the transfer had occurred at the beginning of the earliest reporting period presented. Ameren's historical cost basis in Ameren Illinois included purchase accounting adjustments related to Ameren's acquisition of CILCORP in 2003. Ameren Illinois accounted for the AERG distribution as a spinoff. Ameren Illinois transferred AERG to Ameren based on AERG's carrying value. Ameren Illinois has segregated AERG's operating results and cash flows and presented them separately as discontinued operations in its consolidated statement of income and consolidated statement of cash flows, respectively, for all periods presented prior to October 1, 2010, in this report. For Ameren's financial statements, AERG's results of operations remain classified as continuing operations. See Note 14 - Discontinued Operations for additional information.

Consolidation

The financial statements of Ameren, Ameren Illinois and Genco are prepared on a consolidated basis. Ameren Missouri has no subsidiaries, and therefore its financial statements were not prepared on a consolidated basis. All significant intercompany transactions have been eliminated. All tabular dollar amounts are in millions, unless otherwise indicated.

Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair presentation of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and the reported amounts of revenues and expenses during the reported periods. Actual results could differ from those estimates. The results of operations of an interim period may not give a true indication of results that may be expected for a full year. These financial statements should be read in conjunction with the financial statements and the notes thereto included in the Form 10-K.

Earnings Per Share

Earnings Per Share

There were no material differences between Ameren's basic and diluted earnings per share amounts for the three months and six months ended June 30, 2011, and 2010. The number of restricted stock shares and performance share units outstanding had an immaterial impact on earnings per share.

Long-term Incentive Plan

The fair value of each share unit awarded in January 2011 under the 2006 Plan was determined to be $31.41. That amount was based on Ameren's closing common share price of $28.19 at December 31, 2010, and lattice simulations. Lattice simulations are used to estimate expected share payout based on Ameren's total shareholder return for a three-year performance period relative to the designated peer group beginning January 1, 2011. The significant assumptions used to calculate fair value also included a three-year risk-free rate of 1.08%, volatility of 22% to 36% for the peer group, and Ameren's attainment of a three-year average earnings per share threshold during the performance period.

Ameren recorded compensation expense of $4 million and $2 million for the three months ended June 30, 2011, and 2010, respectively, and a related tax benefit of $2 million and $1 million for the three months ended June 30, 2011, and 2010, respectively. Ameren recorded compensation expense of $7 million for each of the six-month periods ended June 30, 2011, and 2010, respectively, and a related tax benefit of $3 million for each of the six-month periods ended June 30, 2011, and 2010, respectively. As of June 30, 2011, total compensation expense of $27 million related to nonvested awards not yet recognized was expected to be recognized over a weighted-average period of 22 months.

Accounting Changes and Other Matters

Accounting Changes

Disclosures about Fair Value Measurements

See Note 7 - Fair Value Measurements for recently adopted guidance on fair value measurements.

In May 2011, FASB issued authoritative guidance regarding fair value measurements. The guidance amends the disclosure requirements for fair value measurements in order to align the principles for fair value measurements and the related disclosure requirements under GAAP and International Financial Reporting Standards. The amendments will not impact the Ameren Companies' results of operations, financial positions, or liquidity, as this guidance only requires additional disclosures. This guidance will become effective for the Ameren Companies for periods starting after December 31, 2011.

Presentation of Comprehensive Income

In June 2011, FASB amended its guidance on the presentation of comprehensive income in financial statements. The amended guidance with respect to comprehensive income will not impact the Ameren Companies' results of operations, financial positions, or liquidity or the items that must be reported in other comprehensive income or when an item of other comprehensive income must be reclassified to net income. The amended guidance will only change the presentation of comprehensive income in the financial statements. The new accounting guidance requires entities to report components of comprehensive income in either a continuous statement of comprehensive income or two separate but consecutive statements. This guidance will become effective for the Ameren Companies for periods starting after December 31, 2011.

Goodwill and Intangible Assets

Goodwill and Intangible Assets

Goodwill. Goodwill represents the excess of the purchase price of an acquisition over the fair value of the net assets acquired. As of June 30, 2011, Ameren's and Ameren Illinois' goodwill related to the acquisition of IP in 2004 and the acquisition of CILCORP in 2003. We evaluate goodwill for impairment as of October 31 of each year, or more frequently if events or changes in circumstances indicate that the asset might be impaired.

Intangible Assets. Ameren, Ameren Missouri and Genco classify emission allowances and renewable energy credits as intangible assets. We evaluate intangible assets for impairment if events or changes in circumstances indicate that their carrying amount might be impaired.

In July 2011, the EPA issued the CSAPR, which will create new allowances for SO₂ and NO_x emissions, thereby restricting the use of existing SO₂ and NO_x allowances to the acid rain program and NO_x budget trading program, respectively. In anticipation of the CSAPR announcement, observable market prices for existing emission allowances declined materially. Consequently, during the second quarter of 2011, Ameren and Genco recorded a noncash pretax impairment charge to other operations and maintenance expense of $2 million and $1 million, respectively. Ameren Missouri recorded a $1 million impairment of its SO₂ emission allowances by reducing a previously established regulatory liability relating to the SO₂ emission allowances, which had no impact to earnings. See Note 9 - Commitments and Contingencies for additional information on emission allowances and the CSAPR.

Emission allowances are charged to fuel expense as they are used in operations. The following table presents amortization expense based on usage of emission allowances, net of gains from emission allowance sales for Ameren, Ameren Missouri and Genco during the three and six months ended June 30, 2011, and 2010. The table below does not include the intangible asset impairment charges referenced above.

	Three Months						Six Months
	2011			2010			2011			2010
Ameren(a)	$	1		$	7		$	2		$	10
AMO		-			(b	)		-			(b	)
Genco(a)		1			5			2			8
AERG(a)		(b	)		2			(b	)		2

(a) Includes allowances consumed that were recorded through purchase accounting.

(b) Less than $1 million.

At June 30, 2011, Ameren's and Ameren Missouri's intangible assets also included renewable energy credits obtained through wind and solar power purchase agreements. The book value of each of Ameren's and Ameren Missouri's renewable energy credits as of June 30, 2011, was $3 million.

Excise Taxes

Excise Taxes

Excise taxes imposed on us are reflected on Ameren Missouri electric and natural gas customer bills and Ameren Illinois natural gas customer bills. They are recorded gross in Operating Revenues and Operating Expenses - Taxes Other than Income Taxes on the statement of income. Excise taxes reflected on Ameren Illinois electric customer bills are imposed on the consumer and are therefore not included in revenues and expenses. They are recorded as tax collections payable and included in Taxes Accrued on the balance sheet. The following table presents excise taxes recorded in Operating Revenues and Operating Expenses - Taxes Other than Income Taxes for the three and six months ended June 30, 2011 and 2010:

	Three Months				Six Months
	2011		2010		2011		2010
Ameren	$	44	$	44	$	95	$	90
AMO		34		33		63		58
AIC		10		11		32		32

Uncertain Tax Positions

Uncertain Tax Positions

The amount of unrecognized tax benefits as of June 30, 2011, was $198 million, $146 million, $33 million, and $16 million for Ameren, Ameren Missouri, Ameren Illinois and Genco, respectively. The amount of unrecognized tax benefits (detriments) as of June 30, 2011, that would impact the effective tax rate, if recognized, was $2 million, $2 million, $(1) million and $1 million for Ameren, Ameren Missouri, Ameren Illinois and Genco, respectively.

In the second quarter of 2011, final settlement for the 2005 and 2006 years was reached with the Internal Revenue Service, which resulted in the reduction of uncertain tax liabilities by $39 million, $17 million, $12 million and $4 million for Ameren, Ameren Missouri, Ameren Illinois and Genco, respectively. Ameren's federal income tax returns for the years 2007 through 2009 are before the Appeals Office of the Internal Revenue Service.

State income tax returns are generally subject to examination for a period of three years after filing of the return. The Ameren Companies do not currently have material state income tax issues under examination, administrative appeals, or litigation. The state impact of any federal changes remains subject to examination by various states for a period of up to one year after formal notification to the states.

It is reasonably possible that events will occur during the next 12 months that would cause the total amount of unrecognized tax benefits for the Ameren Companies to increase or decrease. However, the Ameren Companies do not believe such increases or decreases would be material to their results of operations, financial position or liquidity.