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Retirement Benefits (Tables)

3 Months Ended

Mar. 31, 2012


	Pension Benefits^(a)						Postretirement Benefits^(a)
	Three Months						Three Months
	2012			2011			2012			2011
Service cost	$	21		$	20		$	6		$	6
Interest cost		43			45			14			15
Expected return on plan assets		(54	)		(54	)		(14	)		(14	)
Amortization of:
Prior service cost (benefit)		—			—			(1	)		(2	)
Actuarial loss		20			11			4			1

Net periodic benefit cost	$	30		$	22		$	9		$	6

(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.

Summary Of Benefit Plan Costs Incurred


	Pension Costs				Postretirement Costs
	Three Months				Three Months
	2012		2011		2012		2011
Ameren Missouri	$	16	$	14	$	5	$	3
Ameren Illinois		10		5		2		2
Genco		3		2		2		1
Other		1		1		—		—

Ameren^(a)	$	30	$	22	$	9	$	6

(a)	Includes amounts for Ameren registrant and nonregistrant subsidiaries.

- Definition

Tabular disclosure of one or more of the entity's defined benefit pension plans or one or more other defined benefit postretirement plans, separately for pension plans and other postretirement benefit plans including the entity's schedule of fair value of plan assets for defined benefit or other postretirement plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e2417-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 158

-Paragraph 4, 7, 16, 20, 21

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5, 6, 7

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e2410-114920

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 55

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=6930749&loc=d3e4179-114921

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e2439-114920

+ Details