Income Taxes (Tables)

12 Months Ended

Dec. 31, 2012

Income Tax Disclosure [Abstract]

Schedule Of Effective Income Tax Rate Reconciliation

The following table presents the principal reasons why the effective income tax rate differed from the statutory federal income tax rate for the years ended December 31, 2012, 2011, and 2010:

	Ameren		Ameren Missouri		Ameren Illinois
2012
Statutory federal income tax rate:	35	%	35	%	35	%
Increases (decreases) from:
Depreciation differences	—		(1	)	—
Amortization of investment tax credit	1		(1	)	(1	)
State tax	5		3		6
Reserve for uncertain tax positions	—		1		—
Effective income tax rate	41	%	37	%	40	%
2011
Statutory federal income tax rate:	35	%	35	%	35	%
Increases (decreases) from:
Depreciation differences	(1	)	(2	)	—
Amortization of investment tax credit	(1	)	(1	)	(1	)
State tax	4		3		5
Other permanent items(a)	—		1		—
Effective income tax rate	37	%	36	%	39	%
2010
Statutory federal income tax rate:	35	%	35	%	35	%
Increases (decreases) from:
Non-deductible impairment of goodwill	32		—		—
Depreciation differences	(4	)	(3	)	—
Amortization of investment tax credit	(2	)	(1	)	(1	)
State tax	8		3		5
Reserve for uncertain tax positions	(1	)	—		—
Tax credits	(3	)	—		—
Change in federal tax law(b)	3		1		—
Effective income tax rate	68	%	35	%	39	%

(a) Permanent items are treated differently for book and tax purposes and primarily include nondeductible expenses related to lobbying and stock issuance expenses for Ameren Missouri.

(b) Relates to change in taxation of prescription drug benefits to retiree participants from the enactment in 2010 of the Patient Protection and Affordable Care Act and the Health Care and Education Reconciliation Act of 2010.

Schedule Of Components Of Income Tax Expense (Benefit)

The following table presents the components of income tax expense (benefit) for the years ended December 31, 2012, 2011, and 2010:

	Ameren(a)			Ameren Missouri			Ameren Illinois
2012
Current taxes:
Federal	$	31		$	(25	)	$	(7	)
State	3			(10		)	(3		)
Deferred taxes:
Federal	(590		)	248			76
State	(117		)	44			30
Deferred investment tax credits, amortization	(7		)	(5		)	(2		)
Total income tax expense (benefit)	$	(680	)	$	252		$	94
2011
Current taxes:
Federal	$	(27	)	$	3		$	(24	)
State	(5		)	2			(4		)
Deferred taxes:
Federal	273			129			123
State	76			31			34
Deferred investment tax credits, amortization	(7		)	(4		)	(2		)
Total income tax expense	$	310		$	161		$	127
2010
Current taxes:
Federal	$	13		$	(14	)	$	(20	)
State	10			(15		)	(5		)
Deferred taxes:
Federal	274			206			132
State	36			27			32
Deferred investment tax credits, amortization	(8		)	(5		)	(2		)
Total income tax expense	$	325		$	199		$	137

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

Schedule Of Deferred Tax Assets And Liabilities Resulting From Temporary Differences

The following table presents the deferred tax assets and deferred tax liabilities recorded as a result of temporary differences at December 31, 2012, and 2011:

	Ameren(a)			Ameren Missouri			Ameren Illinois
2012
Accumulated deferred income taxes, net liability (asset):
Plant related	$	4,201		$	2,386		$	1,106
Long-lived asset impairments	(986		)	—			—
Deferred intercompany tax gain/basis step-up	2			(1		)	39
Regulatory assets, net	73			73			—
Deferred employee benefit costs	(337		)	(84		)	(102		)
Purchase accounting	(10		)	—			(27		)
ARO	(44		)	(7		)	1
Other(b)	(278		)	50			(77		)
Total net accumulated deferred income tax liabilities(c)	$	2,621		$	2,417		$	940
2011
Accumulated deferred income taxes, net liability (asset):
Plant related	$	3,826		$	2,134		$	1,003
Long-lived asset impairments	(15		)	—			—
Deferred intercompany tax gain/basis step-up	3			(1		)	55
Regulatory assets, net	73			73			—
Deferred employee benefit costs	(367		)	(88		)	(109		)
Purchase accounting	35			—			(27		)
ARO	(37		)	—			1
Other	(223		)	6			(86		)
Total net accumulated deferred income tax liabilities(d)	$	3,295		$	2,124		$	837

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

(b) Includes deferred tax assets related to net operating loss and tax credit carryforwards detailed in the table below.

(c) Includes $26 million recorded in "Other current assets" on Ameren Missouri's balance sheet as of December 31, 2012.

(d) Includes $8 million recorded in "Other current assets" on Ameren Missouri's balance sheet as of December 31, 2011.

Schedule Of Net Operating Loss Carryforwards And Tax Credit Carryforwards

The following table presents the components of deferred tax assets relating to net operating loss carryforwards and tax credit carryforwards at December 31, 2012:

	Ameren			Ameren Missouri			Ameren Illinois
Net operating loss carryforwards:
Federal(a)	$	212		$	61		$	61
State(b)	29			3			11
Total net operating loss carryforwards	$	241		$	64		$	72
Tax credit carryforwards:
Federal(c)	$	87		$	11		$	—
State(d)	35			1			1
State valuation allowance(e)	(4		)	(1		)	(1		)
Total tax credit carryforwards	$	118		$	11		$	—

(a) These will begin to expire in 2028.

(b) These will begin to expire in 2017.

(c) These will begin to expire in 2029.

(d) These will begin to expire in 2013.

(e) This balance increased by $2 million, $- million and $1 million for Ameren, Ameren Missouri and Ameren Illinois respectively during 2012.

Schedule Of Changes To Unrecognized Tax Benefits And Related Interest

A reconciliation of the change in the unrecognized tax benefit balance during the years ended December 31, 2010, 2011, and 2012, is as follows:

	Ameren			Ameren Missouri			Ameren Illinois
Unrecognized tax benefits - January 1, 2010	$	135		$	88		$	—
Increases based on tax positions prior to 2010	72			40			27
Decreases based on tax positions prior to 2010	(38		)	(12		)	(2		)
Increases based on tax positions related to 2010	77			48			31
Changes related to settlements with taxing authorities	—			—			—
Decreases related to the lapse of statute of limitations	—			—			—
Unrecognized tax benefits - December 31, 2010	$	246		$	164		$	56
Increases based on tax positions prior to 2011	22			15			—
Decreases based on tax positions prior to 2011	(125		)	(63		)	(41		)
Increases based on tax positions related to 2011	17			13			—
Changes related to settlements with taxing authorities	(10		)	(5		)	(4		)
Decreases related to the lapse of statute of limitations	(2		)	—			—
Unrecognized tax benefits - December 31, 2011	$	148		$	124		$	11
Increases based on tax positions prior to 2012	5			4			—
Decreases based on tax positions prior to 2012	(13		)	(7		)	(1		)
Increases based on tax positions related to 2012	17			15			3
Changes related to settlements with taxing authorities	—			—			—
Decreases related to the lapse of statute of limitations	(1		)	—			—
Unrecognized tax benefits - December 31, 2012	$	156		$	136		$	13
Total unrecognized tax benefits that, if recognized, would affect the effective tax rates as of December 31, 2010	$	—		$	3		$	—
Total unrecognized tax benefits that, if recognized, would affect the effective tax rates as of December 31, 2011	$	1		$	1		$	—
Total unrecognized tax benefits (detriments) that, if recognized, would affect the effective tax rates as of December 31, 2012	$	1		$	3		$	(1	)

Reconciliation Of Changes In Liability For Interest On Unrecognized Tax Benefits

A reconciliation of the change in the liability for interest on unrecognized tax benefits during the years ended December 31, 2010, 2011, and 2012, is as follows:

	Ameren			Ameren Missouri			Ameren Illinois
Liability for interest - January 1, 2010	$	8		$	4		$	—
Interest charges for 2010	9			6			2
Liability for interest - December 31, 2010	$	17		$	10		$	2
Interest income for 2011	(11		)	(3		)	(1		)
Interest payment	(1		)	(1		)	—
Liability for interest - December 31, 2011	$	5		$	6		$	1
Interest charges for 2012	1			2			—
Liability for interest - December 31, 2012	$	6		$	8		$	1