Summary Of Significant Accounting Policies

3 Months Ended

Mar. 31, 2012

Summary Of Significant Accounting Policies

NOTE 1 - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

General

Ameren, headquartered in St. Louis, Missouri, is a public utility holding company under PUHCA 2005, administered by FERC. Ameren's primary assets are the common stock of its subsidiaries. Ameren's subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. These subsidiaries operate, as the case may be, rate-regulated electric generation, transmission and distribution businesses, rate-regulated natural gas transmission and distribution businesses, and merchant electric generation businesses in Missouri and Illinois. Dividends on Ameren's common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren's principal subsidiaries are listed below. Also see the Glossary of Terms and Abbreviations at the front of this report and in the Form 10-K.

• Union Electric Company, or Ameren Missouri, operates a rate-regulated electric generation, transmission and distribution business, and a rate-regulated natural gas transmission and distribution business in Missouri.

• Ameren Illinois Company, or Ameren Illinois, operates a rate-regulated electric and natural gas transmission and distribution business in Illinois.

• AER consists of non-rate-regulated operations, including Genco, AERG, and Marketing Company. Genco operates a merchant electric generation business in Illinois and holds an 80% ownership interest in EEI, which it consolidates for financial reporting purposes.

Ameren has various other subsidiaries responsible for activities such as the provision of shared services.

The financial statements of Ameren and Genco are prepared on a consolidated basis. Ameren Missouri and Ameren Illinois have no subsidiaries, and therefore their financial statements are 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.

During the second quarter 2011, Genco identified an error in the cash flow statement classification of a capital contribution from Ameren that affected Genco's three months ended March 31, 2011, consolidated statements of cash flows. For the three months ended March 31, 2011, Genco's previously reported cash flows provided by operating activities were $100 million, and Genco had no reported cash flows from financing activities. As corrected herein, Genco's cash flows provided by operating activities were $76 million and cash flows provided by financing activities were $24 million. The error was corrected in Genco's six months ended June 30, 2011, consolidated statement of cash flows. This correction had no impact on Ameren's reported consolidated statement of cash flows.

Earnings Per Share

There were no material differences between Ameren's basic and diluted earnings per share amounts for the three months ended March 31, 2012, and 2011. In the first quarter of 2012, potential issuances of common shares related to stock-based compensation plans were excluded from the quarterly diluted earnings per share calculation because the effect was antidilutive. In 2011, the number of dilutive restricted stock shares and performance share units had an immaterial impact on earnings per share.

Stock-based Compensation

A summary of nonvested shares as of March 31, 2012, and changes during the three months ended March 31, 2012, under the 2006 Omnibus Incentive Compensation Plan (2006 Plan) is presented below:

	Performance Share Units
	Share Units			Weighted-average Fair Value Per Unit at Grant Date
Nonvested at January 1, 2012		1,156,831		$	31.70
Granted(a)		717,151			35.68
Forfeitures		(3,897	)		32.94
Vested(b)		(110,729	)		35.68
Nonvested at March 31, 2012		1,759,356		$	33.07

(a) Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in January 2012 under the 2006 Plan.

(b) Share units vested due to retirement eligibility by certain employees. Actual shares issued for retirement-eligible employees will vary depending on actual performance over the three-year measurement period.

The fair value of each share unit awarded in January 2012 under the 2006 Plan was determined to be $35.68. That amount was based on Ameren's closing common share price of $33.13 at December 31, 2011, 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, 2012. The simulations can produce a greater fair value for the share unit than the applicable closing common share price because they include the weighted payout scenarios in which an increase in the share price has occurred. The significant assumptions used to calculate fair value also included a three-year risk-free rate of 0.41%, volatility of 17% to 31% 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 $6 million and a related tax benefit of $2 million for both the three months ended March 31, 2012, and 2011. There were no significant compensation costs capitalized related to the performance share units during the three months ended March 31, 2012, and 2011. As of March 31, 2012, total compensation cost of $32 million related to nonvested awards not yet recognized was expected to be recognized over a weighted-average period of 26 months.

Accounting Changes

Disclosures about Fair Value Measurements

In May 2011, FASB issued additional 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 do not affect the Ameren Companies' results of operations, financial positions, or liquidity, as this guidance only requires additional disclosures. The Ameren Companies adopted this guidance for the first quarter of 2012. See Note 7 - Fair Value Measurements for the required additional disclosures.

Presentation of Comprehensive Income

In June 2011, FASB amended its guidance on the presentation of comprehensive income in financial statements. The amended guidance changes the presentation of comprehensive income in the financial statements. It requires entities to report components of comprehensive income either in a continuous statement of comprehensive income or in two separate but consecutive statements. This guidance was effective for the Ameren Companies beginning in the first quarter of 2012 with retroactive application required. The implementation of the amended guidance did not affect the Ameren Companies' results of operations, financial positions, or liquidity. In December 2011, the FASB amended the guidance to postpone a requirement to present reclassification adjustments by income component until further guidance is issued.

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 March 31, 2012, Ameren's and Ameren Illinois' goodwill related to Ameren's acquisition of IP in 2004 and 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.

At March 31, 2012, Ameren's and Ameren Missouri's intangible assets consisted of 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 was $9 million at March 31, 2012. The book value of each of Ameren's, Ameren Missouri's, and Genco's CAIR emission allowances was immaterial at March 31, 2012.

Renewable energy credits and emission allowances are charged to purchased power expense and fuel expense, respectively, as they are used in operations. The amortization expense based on usage of renewable energy credits and emission allowances was less than $1 million for Ameren, Ameren Missouri, Ameren Illinois, and Genco for the three months ended March 31, 2012, and $2 million, $1 million, and $1 million for Ameren, Ameren Illinois, and Genco, respectively, for the three months ended March 31, 2011. Amortization expense based on Ameren Missouri's usage of renewable energy credits was deferred as a regulatory asset pending recovery from customers through rates.

Excise Taxes

Excise taxes imposed on us are reflected on Ameren Missouri electric and Ameren Missouri and Ameren Illinois natural gas customer bills. They are recorded gross in "Operating Revenues - Electric," "Operating Revenues - Gas" and "Operating Expenses - Taxes other than income taxes" on the statement of income or the statement of income and comprehensive 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 - Electric," "Operating Revenues - Gas" and "Operating Expenses - Taxes other than income taxes" for the three months ended March 31, 2012, and 2011:

		XXXXXX		XXXXXX
	Three Months
	2012		2011
Ameren Missouri	$	27	$	29
Ameren Illinois		18		22
Ameren	$	45	$	51

Uncertain Tax Positions

The amount of unrecognized tax benefits as of March 31, 2012, was $150 million, $125 million, $11 million, and $10 million for Ameren, Ameren Missouri, Ameren Illinois and Genco, respectively. The amount of unrecognized tax benefits (detriments) as of March 31, 2012, that would impact the effective tax rate, if recognized, was $1 million, $1 million, $(1) million and $1 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. Ameren's federal income tax return for the year 2010 is currently under examination. In April 2012, Ameren filed a protest to the Appeals Office of the Internal Revenue Service with respect to certain adjustments proposed as a result of the Internal Revenue Service's audit examination of its 2010 federal income tax return.

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 expected that a partial settlement will be reached with the Appeals Office of the Internal Revenue Service in the next twelve months for the years 2007 through 2009 that would result in a decrease in uncertain tax liabilities. In addition, it is reasonably possible that events will occur during the next twelve 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.

Asset Retirement Obligations

AROs at Ameren, Ameren Missouri, Ameren Illinois and Genco increased compared to December 31, 2011, to reflect the accretion of obligations to their fair values. In addition, Ameren and Genco recorded an additional ARO in the amount of $1 million related to the retirement costs for a Genco coal combustion byproduct storage area during the three months ended March 31, 2012.

Noncontrolling Interest

Ameren's noncontrolling interests comprised the 20% of EEI not owned by Ameren and the preferred stock not subject to mandatory redemption of Ameren's subsidiaries. These noncontrolling interests were classified as a component of equity separate from Ameren's equity in its consolidated balance sheet. Genco's noncontrolling interest comprised the 20% of EEI not owned by Genco. This noncontrolling interest was classified as a component of equity separate from Genco's equity in its consolidated balance sheet.

A reconciliation of the equity changes attributable to the noncontrolling interest at Ameren and Genco for the three months ended March 31, 2012, and 2011, is shown below:

		XXXXXXX			XXXXXXX
	Three Months
	2012			2011
Ameren:
Noncontrolling interest, beginning of period	$	149		$	154
Net income attributable to noncontrolling interest		-			3
Dividends paid to noncontrolling interest holders		(2	)		(2	)
Noncontrolling interest, end of period	$	147		$	155
Genco:
Noncontrolling interest, beginning of period	$	7		$	11
Net income (loss) attributable to noncontrolling interest		(2	)		1
Noncontrolling interest, end of period	$	5		$	12

Medina Valley Sale in 2012

In February 2012, Ameren completed the sale of its Medina Valley energy center's net property and plant for cash proceeds of $16 million and an additional $1 million payment at the two-year anniversary date of the sale if there are no violations of representations and warranties contained in the sale agreement. Ameren recognized a $10 million pretax gain during the first quarter of 2012 from this sale. Medina Valley was included in Ameren's Merchant Generation segment results.

Ameren Illinois Company [Member]

Summary Of Significant Accounting Policies

NOTE 1 - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

General

Ameren, headquartered in St. Louis, Missouri, is a public utility holding company under PUHCA 2005, administered by FERC. Ameren's primary assets are the common stock of its subsidiaries. Ameren's subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. These subsidiaries operate, as the case may be, rate-regulated electric generation, transmission and distribution businesses, rate-regulated natural gas transmission and distribution businesses, and merchant electric generation businesses in Missouri and Illinois. Dividends on Ameren's common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren's principal subsidiaries are listed below. Also see the Glossary of Terms and Abbreviations at the front of this report and in the Form 10-K.

• Union Electric Company, or Ameren Missouri, operates a rate-regulated electric generation, transmission and distribution business, and a rate-regulated natural gas transmission and distribution business in Missouri.

• Ameren Illinois Company, or Ameren Illinois, operates a rate-regulated electric and natural gas transmission and distribution business in Illinois.

• AER consists of non-rate-regulated operations, including Genco, AERG, and Marketing Company. Genco operates a merchant electric generation business in Illinois and holds an 80% ownership interest in EEI, which it consolidates for financial reporting purposes.

Ameren has various other subsidiaries responsible for activities such as the provision of shared services.

The financial statements of Ameren and Genco are prepared on a consolidated basis. Ameren Missouri and Ameren Illinois have no subsidiaries, and therefore their financial statements are 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.

During the second quarter 2011, Genco identified an error in the cash flow statement classification of a capital contribution from Ameren that affected Genco's three months ended March 31, 2011, consolidated statements of cash flows. For the three months ended March 31, 2011, Genco's previously reported cash flows provided by operating activities were $100 million, and Genco had no reported cash flows from financing activities. As corrected herein, Genco's cash flows provided by operating activities were $76 million and cash flows provided by financing activities were $24 million. The error was corrected in Genco's six months ended June 30, 2011, consolidated statement of cash flows. This correction had no impact on Ameren's reported consolidated statement of cash flows.

Earnings Per Share

There were no material differences between Ameren's basic and diluted earnings per share amounts for the three months ended March 31, 2012, and 2011. In the first quarter of 2012, potential issuances of common shares related to stock-based compensation plans were excluded from the quarterly diluted earnings per share calculation because the effect was antidilutive. In 2011, the number of dilutive restricted stock shares and performance share units had an immaterial impact on earnings per share.

Stock-based Compensation

A summary of nonvested shares as of March 31, 2012, and changes during the three months ended March 31, 2012, under the 2006 Omnibus Incentive Compensation Plan (2006 Plan) is presented below:

	Performance Share Units
	Share Units			Weighted-average Fair Value Per Unit at Grant Date
Nonvested at January 1, 2012		1,156,831		$	31.70
Granted(a)		717,151			35.68
Forfeitures		(3,897	)		32.94
Vested(b)		(110,729	)		35.68
Nonvested at March 31, 2012		1,759,356		$	33.07

(a) Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in January 2012 under the 2006 Plan.

(b) Share units vested due to retirement eligibility by certain employees. Actual shares issued for retirement-eligible employees will vary depending on actual performance over the three-year measurement period.

The fair value of each share unit awarded in January 2012 under the 2006 Plan was determined to be $35.68. That amount was based on Ameren's closing common share price of $33.13 at December 31, 2011, 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, 2012. The simulations can produce a greater fair value for the share unit than the applicable closing common share price because they include the weighted payout scenarios in which an increase in the share price has occurred. The significant assumptions used to calculate fair value also included a three-year risk-free rate of 0.41%, volatility of 17% to 31% 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 $6 million and a related tax benefit of $2 million for both the three months ended March 31, 2012, and 2011. There were no significant compensation costs capitalized related to the performance share units during the three months ended March 31, 2012, and 2011. As of March 31, 2012, total compensation cost of $32 million related to nonvested awards not yet recognized was expected to be recognized over a weighted-average period of 26 months.

Accounting Changes

Disclosures about Fair Value Measurements

In May 2011, FASB issued additional 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 do not affect the Ameren Companies' results of operations, financial positions, or liquidity, as this guidance only requires additional disclosures. The Ameren Companies adopted this guidance for the first quarter of 2012. See Note 7 - Fair Value Measurements for the required additional disclosures.

Presentation of Comprehensive Income

In June 2011, FASB amended its guidance on the presentation of comprehensive income in financial statements. The amended guidance changes the presentation of comprehensive income in the financial statements. It requires entities to report components of comprehensive income either in a continuous statement of comprehensive income or in two separate but consecutive statements. This guidance was effective for the Ameren Companies beginning in the first quarter of 2012 with retroactive application required. The implementation of the amended guidance did not affect the Ameren Companies' results of operations, financial positions, or liquidity. In December 2011, the FASB amended the guidance to postpone a requirement to present reclassification adjustments by income component until further guidance is issued.

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 March 31, 2012, Ameren's and Ameren Illinois' goodwill related to Ameren's acquisition of IP in 2004 and 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.

At March 31, 2012, Ameren's and Ameren Missouri's intangible assets consisted of 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 was $9 million at March 31, 2012. The book value of each of Ameren's, Ameren Missouri's, and Genco's CAIR emission allowances was immaterial at March 31, 2012.

Renewable energy credits and emission allowances are charged to purchased power expense and fuel expense, respectively, as they are used in operations. The amortization expense based on usage of renewable energy credits and emission allowances was less than $1 million for Ameren, Ameren Missouri, Ameren Illinois, and Genco for the three months ended March 31, 2012, and $2 million, $1 million, and $1 million for Ameren, Ameren Illinois, and Genco, respectively, for the three months ended March 31, 2011. Amortization expense based on Ameren Missouri's usage of renewable energy credits was deferred as a regulatory asset pending recovery from customers through rates.

Excise Taxes

Excise taxes imposed on us are reflected on Ameren Missouri electric and Ameren Missouri and Ameren Illinois natural gas customer bills. They are recorded gross in "Operating Revenues - Electric," "Operating Revenues - Gas" and "Operating Expenses - Taxes other than income taxes" on the statement of income or the statement of income and comprehensive 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 - Electric," "Operating Revenues - Gas" and "Operating Expenses - Taxes other than income taxes" for the three months ended March 31, 2012, and 2011:

		XXXXXX		XXXXXX
	Three Months
	2012		2011
Ameren Missouri	$	27	$	29
Ameren Illinois		18		22
Ameren	$	45	$	51

Uncertain Tax Positions

The amount of unrecognized tax benefits as of March 31, 2012, was $150 million, $125 million, $11 million, and $10 million for Ameren, Ameren Missouri, Ameren Illinois and Genco, respectively. The amount of unrecognized tax benefits (detriments) as of March 31, 2012, that would impact the effective tax rate, if recognized, was $1 million, $1 million, $(1) million and $1 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. Ameren's federal income tax return for the year 2010 is currently under examination. In April 2012, Ameren filed a protest to the Appeals Office of the Internal Revenue Service with respect to certain adjustments proposed as a result of the Internal Revenue Service's audit examination of its 2010 federal income tax return.

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 expected that a partial settlement will be reached with the Appeals Office of the Internal Revenue Service in the next twelve months for the years 2007 through 2009 that would result in a decrease in uncertain tax liabilities. In addition, it is reasonably possible that events will occur during the next twelve 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.

Asset Retirement Obligations

AROs at Ameren, Ameren Missouri, Ameren Illinois and Genco increased compared to December 31, 2011, to reflect the accretion of obligations to their fair values. In addition, Ameren and Genco recorded an additional ARO in the amount of $1 million related to the retirement costs for a Genco coal combustion byproduct storage area during the three months ended March 31, 2012.

Noncontrolling Interest

Ameren's noncontrolling interests comprised the 20% of EEI not owned by Ameren and the preferred stock not subject to mandatory redemption of Ameren's subsidiaries. These noncontrolling interests were classified as a component of equity separate from Ameren's equity in its consolidated balance sheet. Genco's noncontrolling interest comprised the 20% of EEI not owned by Genco. This noncontrolling interest was classified as a component of equity separate from Genco's equity in its consolidated balance sheet.

A reconciliation of the equity changes attributable to the noncontrolling interest at Ameren and Genco for the three months ended March 31, 2012, and 2011, is shown below:

		XXXXXXX			XXXXXXX
	Three Months
	2012			2011
Ameren:
Noncontrolling interest, beginning of period	$	149		$	154
Net income attributable to noncontrolling interest		-			3
Dividends paid to noncontrolling interest holders		(2	)		(2	)
Noncontrolling interest, end of period	$	147		$	155
Genco:
Noncontrolling interest, beginning of period	$	7		$	11
Net income (loss) attributable to noncontrolling interest		(2	)		1
Noncontrolling interest, end of period	$	5		$	12

Medina Valley Sale in 2012

In February 2012, Ameren completed the sale of its Medina Valley energy center's net property and plant for cash proceeds of $16 million and an additional $1 million payment at the two-year anniversary date of the sale if there are no violations of representations and warranties contained in the sale agreement. Ameren recognized a $10 million pretax gain during the first quarter of 2012 from this sale. Medina Valley was included in Ameren's Merchant Generation segment results.

Ameren Energy Generating Company [Member]

Summary Of Significant Accounting Policies

NOTE 1 - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

General

Ameren, headquartered in St. Louis, Missouri, is a public utility holding company under PUHCA 2005, administered by FERC. Ameren's primary assets are the common stock of its subsidiaries. Ameren's subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. These subsidiaries operate, as the case may be, rate-regulated electric generation, transmission and distribution businesses, rate-regulated natural gas transmission and distribution businesses, and merchant electric generation businesses in Missouri and Illinois. Dividends on Ameren's common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren's principal subsidiaries are listed below. Also see the Glossary of Terms and Abbreviations at the front of this report and in the Form 10-K.

• Union Electric Company, or Ameren Missouri, operates a rate-regulated electric generation, transmission and distribution business, and a rate-regulated natural gas transmission and distribution business in Missouri.

• Ameren Illinois Company, or Ameren Illinois, operates a rate-regulated electric and natural gas transmission and distribution business in Illinois.

• AER consists of non-rate-regulated operations, including Genco, AERG, and Marketing Company. Genco operates a merchant electric generation business in Illinois and holds an 80% ownership interest in EEI, which it consolidates for financial reporting purposes.

Ameren has various other subsidiaries responsible for activities such as the provision of shared services.

The financial statements of Ameren and Genco are prepared on a consolidated basis. Ameren Missouri and Ameren Illinois have no subsidiaries, and therefore their financial statements are 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.

During the second quarter 2011, Genco identified an error in the cash flow statement classification of a capital contribution from Ameren that affected Genco's three months ended March 31, 2011, consolidated statements of cash flows. For the three months ended March 31, 2011, Genco's previously reported cash flows provided by operating activities were $100 million, and Genco had no reported cash flows from financing activities. As corrected herein, Genco's cash flows provided by operating activities were $76 million and cash flows provided by financing activities were $24 million. The error was corrected in Genco's six months ended June 30, 2011, consolidated statement of cash flows. This correction had no impact on Ameren's reported consolidated statement of cash flows.

Earnings Per Share

There were no material differences between Ameren's basic and diluted earnings per share amounts for the three months ended March 31, 2012, and 2011. In the first quarter of 2012, potential issuances of common shares related to stock-based compensation plans were excluded from the quarterly diluted earnings per share calculation because the effect was antidilutive. In 2011, the number of dilutive restricted stock shares and performance share units had an immaterial impact on earnings per share.

Stock-based Compensation

A summary of nonvested shares as of March 31, 2012, and changes during the three months ended March 31, 2012, under the 2006 Omnibus Incentive Compensation Plan (2006 Plan) is presented below:

	Performance Share Units
	Share Units			Weighted-average Fair Value Per Unit at Grant Date
Nonvested at January 1, 2012		1,156,831		$	31.70
Granted(a)		717,151			35.68
Forfeitures		(3,897	)		32.94
Vested(b)		(110,729	)		35.68
Nonvested at March 31, 2012		1,759,356		$	33.07

(a) Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in January 2012 under the 2006 Plan.

(b) Share units vested due to retirement eligibility by certain employees. Actual shares issued for retirement-eligible employees will vary depending on actual performance over the three-year measurement period.

The fair value of each share unit awarded in January 2012 under the 2006 Plan was determined to be $35.68. That amount was based on Ameren's closing common share price of $33.13 at December 31, 2011, 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, 2012. The simulations can produce a greater fair value for the share unit than the applicable closing common share price because they include the weighted payout scenarios in which an increase in the share price has occurred. The significant assumptions used to calculate fair value also included a three-year risk-free rate of 0.41%, volatility of 17% to 31% 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 $6 million and a related tax benefit of $2 million for both the three months ended March 31, 2012, and 2011. There were no significant compensation costs capitalized related to the performance share units during the three months ended March 31, 2012, and 2011. As of March 31, 2012, total compensation cost of $32 million related to nonvested awards not yet recognized was expected to be recognized over a weighted-average period of 26 months.

Accounting Changes

Disclosures about Fair Value Measurements

In May 2011, FASB issued additional 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 do not affect the Ameren Companies' results of operations, financial positions, or liquidity, as this guidance only requires additional disclosures. The Ameren Companies adopted this guidance for the first quarter of 2012. See Note 7 - Fair Value Measurements for the required additional disclosures.

Presentation of Comprehensive Income

In June 2011, FASB amended its guidance on the presentation of comprehensive income in financial statements. The amended guidance changes the presentation of comprehensive income in the financial statements. It requires entities to report components of comprehensive income either in a continuous statement of comprehensive income or in two separate but consecutive statements. This guidance was effective for the Ameren Companies beginning in the first quarter of 2012 with retroactive application required. The implementation of the amended guidance did not affect the Ameren Companies' results of operations, financial positions, or liquidity. In December 2011, the FASB amended the guidance to postpone a requirement to present reclassification adjustments by income component until further guidance is issued.

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 March 31, 2012, Ameren's and Ameren Illinois' goodwill related to Ameren's acquisition of IP in 2004 and 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.

At March 31, 2012, Ameren's and Ameren Missouri's intangible assets consisted of 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 was $9 million at March 31, 2012. The book value of each of Ameren's, Ameren Missouri's, and Genco's CAIR emission allowances was immaterial at March 31, 2012.

Renewable energy credits and emission allowances are charged to purchased power expense and fuel expense, respectively, as they are used in operations. The amortization expense based on usage of renewable energy credits and emission allowances was less than $1 million for Ameren, Ameren Missouri, Ameren Illinois, and Genco for the three months ended March 31, 2012, and $2 million, $1 million, and $1 million for Ameren, Ameren Illinois, and Genco, respectively, for the three months ended March 31, 2011. Amortization expense based on Ameren Missouri's usage of renewable energy credits was deferred as a regulatory asset pending recovery from customers through rates.

Excise Taxes

Excise taxes imposed on us are reflected on Ameren Missouri electric and Ameren Missouri and Ameren Illinois natural gas customer bills. They are recorded gross in "Operating Revenues - Electric," "Operating Revenues - Gas" and "Operating Expenses - Taxes other than income taxes" on the statement of income or the statement of income and comprehensive 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 - Electric," "Operating Revenues - Gas" and "Operating Expenses - Taxes other than income taxes" for the three months ended March 31, 2012, and 2011:

		XXXXXX		XXXXXX
	Three Months
	2012		2011
Ameren Missouri	$	27	$	29
Ameren Illinois		18		22
Ameren	$	45	$	51

Uncertain Tax Positions

The amount of unrecognized tax benefits as of March 31, 2012, was $150 million, $125 million, $11 million, and $10 million for Ameren, Ameren Missouri, Ameren Illinois and Genco, respectively. The amount of unrecognized tax benefits (detriments) as of March 31, 2012, that would impact the effective tax rate, if recognized, was $1 million, $1 million, $(1) million and $1 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. Ameren's federal income tax return for the year 2010 is currently under examination. In April 2012, Ameren filed a protest to the Appeals Office of the Internal Revenue Service with respect to certain adjustments proposed as a result of the Internal Revenue Service's audit examination of its 2010 federal income tax return.

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 expected that a partial settlement will be reached with the Appeals Office of the Internal Revenue Service in the next twelve months for the years 2007 through 2009 that would result in a decrease in uncertain tax liabilities. In addition, it is reasonably possible that events will occur during the next twelve 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.

Asset Retirement Obligations

AROs at Ameren, Ameren Missouri, Ameren Illinois and Genco increased compared to December 31, 2011, to reflect the accretion of obligations to their fair values. In addition, Ameren and Genco recorded an additional ARO in the amount of $1 million related to the retirement costs for a Genco coal combustion byproduct storage area during the three months ended March 31, 2012.

Noncontrolling Interest

Ameren's noncontrolling interests comprised the 20% of EEI not owned by Ameren and the preferred stock not subject to mandatory redemption of Ameren's subsidiaries. These noncontrolling interests were classified as a component of equity separate from Ameren's equity in its consolidated balance sheet. Genco's noncontrolling interest comprised the 20% of EEI not owned by Genco. This noncontrolling interest was classified as a component of equity separate from Genco's equity in its consolidated balance sheet.

A reconciliation of the equity changes attributable to the noncontrolling interest at Ameren and Genco for the three months ended March 31, 2012, and 2011, is shown below:

		XXXXXXX			XXXXXXX
	Three Months
	2012			2011
Ameren:
Noncontrolling interest, beginning of period	$	149		$	154
Net income attributable to noncontrolling interest		-			3
Dividends paid to noncontrolling interest holders		(2	)		(2	)
Noncontrolling interest, end of period	$	147		$	155
Genco:
Noncontrolling interest, beginning of period	$	7		$	11
Net income (loss) attributable to noncontrolling interest		(2	)		1
Noncontrolling interest, end of period	$	5		$	12

Medina Valley Sale in 2012

In February 2012, Ameren completed the sale of its Medina Valley energy center's net property and plant for cash proceeds of $16 million and an additional $1 million payment at the two-year anniversary date of the sale if there are no violations of representations and warranties contained in the sale agreement. Ameren recognized a $10 million pretax gain during the first quarter of 2012 from this sale. Medina Valley was included in Ameren's Merchant Generation segment results.

Union Electric Company [Member]

Summary Of Significant Accounting Policies

NOTE 1 - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

General

Ameren, headquartered in St. Louis, Missouri, is a public utility holding company under PUHCA 2005, administered by FERC. Ameren's primary assets are the common stock of its subsidiaries. Ameren's subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. These subsidiaries operate, as the case may be, rate-regulated electric generation, transmission and distribution businesses, rate-regulated natural gas transmission and distribution businesses, and merchant electric generation businesses in Missouri and Illinois. Dividends on Ameren's common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren's principal subsidiaries are listed below. Also see the Glossary of Terms and Abbreviations at the front of this report and in the Form 10-K.

• Union Electric Company, or Ameren Missouri, operates a rate-regulated electric generation, transmission and distribution business, and a rate-regulated natural gas transmission and distribution business in Missouri.

• Ameren Illinois Company, or Ameren Illinois, operates a rate-regulated electric and natural gas transmission and distribution business in Illinois.

• AER consists of non-rate-regulated operations, including Genco, AERG, and Marketing Company. Genco operates a merchant electric generation business in Illinois and holds an 80% ownership interest in EEI, which it consolidates for financial reporting purposes.

Ameren has various other subsidiaries responsible for activities such as the provision of shared services.

The financial statements of Ameren and Genco are prepared on a consolidated basis. Ameren Missouri and Ameren Illinois have no subsidiaries, and therefore their financial statements are 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.

During the second quarter 2011, Genco identified an error in the cash flow statement classification of a capital contribution from Ameren that affected Genco's three months ended March 31, 2011, consolidated statements of cash flows. For the three months ended March 31, 2011, Genco's previously reported cash flows provided by operating activities were $100 million, and Genco had no reported cash flows from financing activities. As corrected herein, Genco's cash flows provided by operating activities were $76 million and cash flows provided by financing activities were $24 million. The error was corrected in Genco's six months ended June 30, 2011, consolidated statement of cash flows. This correction had no impact on Ameren's reported consolidated statement of cash flows.

Earnings Per Share

There were no material differences between Ameren's basic and diluted earnings per share amounts for the three months ended March 31, 2012, and 2011. In the first quarter of 2012, potential issuances of common shares related to stock-based compensation plans were excluded from the quarterly diluted earnings per share calculation because the effect was antidilutive. In 2011, the number of dilutive restricted stock shares and performance share units had an immaterial impact on earnings per share.

Stock-based Compensation

A summary of nonvested shares as of March 31, 2012, and changes during the three months ended March 31, 2012, under the 2006 Omnibus Incentive Compensation Plan (2006 Plan) is presented below:

	Performance Share Units
	Share Units			Weighted-average Fair Value Per Unit at Grant Date
Nonvested at January 1, 2012		1,156,831		$	31.70
Granted(a)		717,151			35.68
Forfeitures		(3,897	)		32.94
Vested(b)		(110,729	)		35.68
Nonvested at March 31, 2012		1,759,356		$	33.07

(a) Includes performance share units (share units) granted to certain executive and nonexecutive officers and other eligible employees in January 2012 under the 2006 Plan.

(b) Share units vested due to retirement eligibility by certain employees. Actual shares issued for retirement-eligible employees will vary depending on actual performance over the three-year measurement period.

The fair value of each share unit awarded in January 2012 under the 2006 Plan was determined to be $35.68. That amount was based on Ameren's closing common share price of $33.13 at December 31, 2011, 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, 2012. The simulations can produce a greater fair value for the share unit than the applicable closing common share price because they include the weighted payout scenarios in which an increase in the share price has occurred. The significant assumptions used to calculate fair value also included a three-year risk-free rate of 0.41%, volatility of 17% to 31% 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 $6 million and a related tax benefit of $2 million for both the three months ended March 31, 2012, and 2011. There were no significant compensation costs capitalized related to the performance share units during the three months ended March 31, 2012, and 2011. As of March 31, 2012, total compensation cost of $32 million related to nonvested awards not yet recognized was expected to be recognized over a weighted-average period of 26 months.

Accounting Changes

Disclosures about Fair Value Measurements

In May 2011, FASB issued additional 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 do not affect the Ameren Companies' results of operations, financial positions, or liquidity, as this guidance only requires additional disclosures. The Ameren Companies adopted this guidance for the first quarter of 2012. See Note 7 - Fair Value Measurements for the required additional disclosures.

Presentation of Comprehensive Income

In June 2011, FASB amended its guidance on the presentation of comprehensive income in financial statements. The amended guidance changes the presentation of comprehensive income in the financial statements. It requires entities to report components of comprehensive income either in a continuous statement of comprehensive income or in two separate but consecutive statements. This guidance was effective for the Ameren Companies beginning in the first quarter of 2012 with retroactive application required. The implementation of the amended guidance did not affect the Ameren Companies' results of operations, financial positions, or liquidity. In December 2011, the FASB amended the guidance to postpone a requirement to present reclassification adjustments by income component until further guidance is issued.

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 March 31, 2012, Ameren's and Ameren Illinois' goodwill related to Ameren's acquisition of IP in 2004 and 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.

At March 31, 2012, Ameren's and Ameren Missouri's intangible assets consisted of 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 was $9 million at March 31, 2012. The book value of each of Ameren's, Ameren Missouri's, and Genco's CAIR emission allowances was immaterial at March 31, 2012.

Renewable energy credits and emission allowances are charged to purchased power expense and fuel expense, respectively, as they are used in operations. The amortization expense based on usage of renewable energy credits and emission allowances was less than $1 million for Ameren, Ameren Missouri, Ameren Illinois, and Genco for the three months ended March 31, 2012, and $2 million, $1 million, and $1 million for Ameren, Ameren Illinois, and Genco, respectively, for the three months ended March 31, 2011. Amortization expense based on Ameren Missouri's usage of renewable energy credits was deferred as a regulatory asset pending recovery from customers through rates.

Excise Taxes

Excise taxes imposed on us are reflected on Ameren Missouri electric and Ameren Missouri and Ameren Illinois natural gas customer bills. They are recorded gross in "Operating Revenues - Electric," "Operating Revenues - Gas" and "Operating Expenses - Taxes other than income taxes" on the statement of income or the statement of income and comprehensive 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 - Electric," "Operating Revenues - Gas" and "Operating Expenses - Taxes other than income taxes" for the three months ended March 31, 2012, and 2011:

		XXXXXX		XXXXXX
	Three Months
	2012		2011
Ameren Missouri	$	27	$	29
Ameren Illinois		18		22
Ameren	$	45	$	51

Uncertain Tax Positions

The amount of unrecognized tax benefits as of March 31, 2012, was $150 million, $125 million, $11 million, and $10 million for Ameren, Ameren Missouri, Ameren Illinois and Genco, respectively. The amount of unrecognized tax benefits (detriments) as of March 31, 2012, that would impact the effective tax rate, if recognized, was $1 million, $1 million, $(1) million and $1 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. Ameren's federal income tax return for the year 2010 is currently under examination. In April 2012, Ameren filed a protest to the Appeals Office of the Internal Revenue Service with respect to certain adjustments proposed as a result of the Internal Revenue Service's audit examination of its 2010 federal income tax return.

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 expected that a partial settlement will be reached with the Appeals Office of the Internal Revenue Service in the next twelve months for the years 2007 through 2009 that would result in a decrease in uncertain tax liabilities. In addition, it is reasonably possible that events will occur during the next twelve 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.

Asset Retirement Obligations

AROs at Ameren, Ameren Missouri, Ameren Illinois and Genco increased compared to December 31, 2011, to reflect the accretion of obligations to their fair values. In addition, Ameren and Genco recorded an additional ARO in the amount of $1 million related to the retirement costs for a Genco coal combustion byproduct storage area during the three months ended March 31, 2012.

Noncontrolling Interest

Ameren's noncontrolling interests comprised the 20% of EEI not owned by Ameren and the preferred stock not subject to mandatory redemption of Ameren's subsidiaries. These noncontrolling interests were classified as a component of equity separate from Ameren's equity in its consolidated balance sheet. Genco's noncontrolling interest comprised the 20% of EEI not owned by Genco. This noncontrolling interest was classified as a component of equity separate from Genco's equity in its consolidated balance sheet.

A reconciliation of the equity changes attributable to the noncontrolling interest at Ameren and Genco for the three months ended March 31, 2012, and 2011, is shown below:

		XXXXXXX			XXXXXXX
	Three Months
	2012			2011
Ameren:
Noncontrolling interest, beginning of period	$	149		$	154
Net income attributable to noncontrolling interest		-			3
Dividends paid to noncontrolling interest holders		(2	)		(2	)
Noncontrolling interest, end of period	$	147		$	155
Genco:
Noncontrolling interest, beginning of period	$	7		$	11
Net income (loss) attributable to noncontrolling interest		(2	)		1
Noncontrolling interest, end of period	$	5		$	12

Medina Valley Sale in 2012

In February 2012, Ameren completed the sale of its Medina Valley energy center's net property and plant for cash proceeds of $16 million and an additional $1 million payment at the two-year anniversary date of the sale if there are no violations of representations and warranties contained in the sale agreement. Ameren recognized a $10 million pretax gain during the first quarter of 2012 from this sale. Medina Valley was included in Ameren's Merchant Generation segment results.