Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2012

Fair Value Disclosures [Abstract]

Fair Value Inputs, Assets and Liabilities, Quantitative Information

The following table describes the valuation techniques and unobservable inputs for the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy for the period ended December 31, 2012:

		Fair Value							Range [Weighted
		Assets		Liabilities			Valuation Technique(s)	Unobservable Input	Average]
Level 3 Derivative asset and liability - commodity contracts(a):
Ameren(b)	Fuel oils	$	9	$	(3	)	Discounted cash flow	Escalation rate(%)(c)	.21 - .68 [.48]
								Counterparty credit risk(%)(d),(e)	.12 - 1 [1]
								Ameren credit risk(%)(d),(e)	2 - 31 [12]
							Option model	Volatilities(%)(c)	7 - 27 [24]
	Power(f)	131		(172		)	Option model	Volatilities(%)(d)	13 - 38 [26]
								Average bid/ask consensus peak and off-peak pricing($/MWh)(d)	24 - 45 [36]
							Discounted cash flow	Average bid/ask consensus peak and off-peak pricing - forwards/swaps($/MWh)(d)	16 - 52 [32]
								Estimated auction price for FTRs($/MW)(c)	(133,787) - 19,671 [198]
								Nodal basis($/MWh)(d)	(12) - 1 [(1)]
								Counterparty credit risk(%)(d),(e)	.04 - 100 [2]
								Ameren credit risk(%)(d),(e)	2 - 5 [5]
							Fundamental energy production model	Estimated future gas prices($/mmbtu)(c)	4 - 8 [6]
							Contract price allocation	Estimated renewable energy credit costs($/credit)(c)	5 - 7 [6]
	Uranium	—		(2		)	Discounted cash flow	Average bid/ask consensus pricing($/pound)(c)	43 - 46 [44]
Ameren Missouri	Fuel oils	$	8	$	(3	)	Discounted cash flow	Escalation rate(%)(c)	.21 - .60 [.44]
								Counterparty credit risk(%)(d),(e)	.12 - 1 [1]
								Ameren Missouri credit risk(%)(d),(e)	2
							Option model	Volatilities(%)(c)	7 - 27 [24]
	Power(f)	14		(3		)	Discounted cash flow	Average bid/ask consensus peak and off-peak pricing - forwards/swaps($/MWh)(d)	24 - 56 [36]
								Estimated auction price for FTRs($/MW)(c)	(281) - 1,851 [178]
								Nodal basis($/MWh)(d)	(5) - (1) [(2)]
								Counterparty credit risk(%)(d),(e)	.22 - 1 [1]
								Ameren Missouri credit risk(%)(d),(e)	2
	Uranium	—		(2		)	Discounted cash flow	Average bid/ask consensus pricing($/pound)(c)	43 - 46 [44]
Ameren Illinois	Power(f)	$	—	$	(111	)	Discounted cash flow	Average bid/ask consensus peak and off-peak pricing - forwards/swaps($/MWh)(c)	22 - 47 [30]
								Nodal basis($/MWh)(c)	(5) - (1) [(3)]
								Ameren Illinois credit risk(%)(d),(e)	5
							Fundamental energy production model	Estimated future gas prices($/mmbtu)(c)	4 - 8 [6]
							Contract price allocation	Estimated renewable energy credit costs($/credit)(c)	5 - 7 [6]

(a) The derivative asset and liability balances are presented net of counterparty credit considerations.

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

(c) Generally, significant increases (decreases) in this input in isolation would result in a significantly higher (lower) fair value measurement.

(d) Generally, significant increases (decreases) in this input in isolation would result in a significantly lower (higher) fair value measurement.

(e) Counterparty credit risk is only applied to counterparties with derivative asset balances. Ameren, Ameren Missouri, and Ameren Illinois credit risk is only applied to counterparties with derivative liability balances.

(f) Power valuations utilize visible third party pricing evaluated by month for peak and off-peak through 2017. Valuations beyond 2017 utilize fundamentally modeled pricing by month for peak and off-peak.

Schedule Of Fair Value Hierarchy Of Assets And Liabilities Measured At Fair Value On Recurring Basis

The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of December 31, 2012:

		Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Other Unobservable Inputs (Level 3)		Total
Assets:
Ameren(a)	Derivative assets - commodity contracts(b):
	Coal	$	1	$	—	$	—	$	1
	Fuel oils	6		—		9		15
	Natural gas	4		2		—		6
	Power	—		9		131		140
	Total derivative assets - commodity contracts	$	11	$	11	$	140	$	162
	Nuclear decommissioning trust fund(c):
	Cash and cash equivalents	1		—		—		1
	Equity securities:
	U.S. large capitalization	264		—		—		264
	Debt securities:
	Corporate bonds	—		47		—		47
	Municipal bonds	—		1		—		1
	U.S. treasury and agency securities	—		81		—		81
	Asset-backed securities	—		11		—		11
	Other	—		1		—		1
	Total nuclear decommissioning trust fund	$	265	$	141	$	—	$	406
	Total Ameren	$	276	$	152	$	140	$	568

Ameren Missouri	Derivative assets - commodity contracts(b):
	Fuel oils	$	4	$	—	$	8	$	12
	Natural gas	—		1		—		1
	Power	—		1		14		15
	Total derivative assets - commodity contracts	$	4	$	2	$	22	$	28
	Nuclear decommissioning trust fund(c):
	Cash and cash equivalents	1		—		—		1
	Equity securities:
	U.S. large capitalization	264		—		—		264
	Debt securities:
	Corporate bonds	—		47		—		47
	Municipal bonds	—		1		—		1
	U.S. treasury and agency securities	—		81		—		81
	Asset-backed securities	—		11		—		11
	Other	—		1		—		1
	Total nuclear decommissioning trust fund	$	265	$	141	$	—	$	406
	Total Ameren Missouri	$	269	$	143	$	22	$	434
Ameren Illinois	Derivative assets - commodity contracts(b):
	Natural gas	$	—	$	1	$	—	$	1
	Power	—		—		—		—
	Total Ameren Illinois	$	—	$	1	$	—	$	1
Liabilities:
Ameren(a)	Derivative liabilities - commodity contracts(b):
	Coal	$	13	$	—	$	—	$	13
	Fuel oils	3		—		3		6
	Natural gas	11		102		—		113
	Power	—		9		172		181
	Uranium	—		—		2		2
	Total Ameren	$	27	$	111	$	177	$	315
Ameren Missouri	Derivative liabilities - commodity contracts(b):
	Fuel oils	$	1	$	—	$	3	$	4
	Natural gas	7		8		—		15
	Power	—		1		3		4
	Uranium	—		—		2		2
	Total Ameren Missouri	$	8	$	9	$	8	$	25
Ameren Illinois	Derivative liabilities - commodity contracts(b):
	Natural gas	$	—	$	94	$	—	$	94
	Power	—		—		111		111
	Total Ameren Illinois	$	—	$	94	$	111	$	205

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

(b) The derivative asset and liability balances are presented net of counterparty credit considerations.

(c) Balance excludes $2 million of receivables, payables, and accrued income, net.

The following table sets forth, by level within the fair value hierarchy, our assets and liabilities measured at fair value on a recurring basis as of December 31, 2011:

		Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Other Unobservable Inputs (Level 3)		Total
Assets:
Ameren(a)	Derivative assets - commodity contracts(b):
	Fuel oils	$	33	$	—	$	4	$	37
	Natural gas	4		—		2		6
	Power	—		2		193		195

	Total derivative assets - commodity contracts	$	37	$	2	$	199	$	238
	Nuclear decommissioning trust fund(c):
	Cash and cash equivalents	3		—		—		3
	Equity securities:
	U.S. large capitalization	234		—		—		234
	Debt securities:
	Corporate bonds	—		44		—		44
	Municipal bonds	—		1		—		1
	U.S. treasury and agency securities	—		65		—		65
	Asset-backed securities	—		10		—		10
	Other	—		1		—		1
	Total nuclear decommissioning trust fund	$	237	$	121	$	—	$	358
	Total Ameren	$	274	$	123	$	199	$	596
Ameren Missouri	Derivative assets - commodity contracts(b):
	Fuel oils	$	20	$	—	$	3	$	23
	Natural gas	2		—		—		2
	Power	—		1		29		30
	Total derivative assets - commodity contracts	$	22	$	1	$	32	$	55
	Nuclear decommissioning trust fund(c):
	Cash and cash equivalents	3		—		—		3
	Equity securities:
	U.S. large capitalization	234		—		—		234
	Debt securities:
	Corporate bonds	—		44		—		44
	Municipal bonds	—		1		—		1
	U.S. treasury and agency securities	—		65		—		65
	Asset-backed securities	—		10		—		10
	Other	—		1		—		1
	Total nuclear decommissioning trust fund	$	237	$	121	$	—	$	358
	Total Ameren Missouri	$	259	$	122	$	32	$	413
Ameren Illinois	Derivative assets - commodity contracts(b):
	Natural gas	$	—	$	—	$	2	$	2
	Power	—		—		77		77
	Total Ameren Illinois	$	—	$	—	$	79	$	79
Liabilities:
Ameren(a)	Derivative liabilities - commodity contracts(b):
	Fuel oils	$	2	$	—	$	—	$	2
	Natural gas	22		—		176		198
	Power	—		2		78		80
	Uranium	—		—		1		1
	Total Ameren	$	24	$	2	$	255	$	281
Ameren Missouri	Derivative liabilities - commodity contracts(b):
	Fuel oils	$	1	$	—	$	—	$	1
	Natural gas	12		—		14		26
	Power	—		1		8		9
	Uranium	—		—		1		1
	Total Ameren Missouri	$	13	$	1	$	23	$	37
Ameren Illinois	Derivative liabilities - commodity contracts(b):
	Natural gas	$	7	$	—	$	162	$	169
	Power	—		—		217		217
	Total Ameren Illinois	$	7	$	—	$	379	$	386

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

(b) The derivative asset and liability balances are presented net of counterparty credit considerations.

(c) Balance excludes $(1) million of receivables, payables, and accrued income, net.

Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level 3 In The Fair Value Hierarchy

The following table summarizes the changes in the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy as of December 31, 2012:

		Net Derivative Commodity Contracts
		Ameren Missouri			Ameren Illinois			Other(a)			Ameren
Fuel oils:
Beginning balance at January 1, 2012	$	3		$	(b)		$	1		$	4
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		(1	)		(b)			(b)			(1	)
Total realized and unrealized gains (losses)		(1	)		(b)			(b)			(1	)
Purchases		7			(b)			—			7
Sales		(3	)		(b)			—			(3	)
Settlements		(2	)		(b)			—			(2	)
Transfers into Level 3		1			(b)			1			2
Transfers out of Level 3		—			(b)			(1	)		(1	)
Ending balance at December 31, 2012	$	5		$	(b)		$	1		$	6
Change in unrealized gains (losses) related to assets/liabilities held at December 31,2012	$	(1	)	$	(b)		$	—		$	(1	)
Natural gas:
Beginning balance at January 1, 2012	$	(14	)	$	(160	)	$	—		$	(174	)
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		(2	)		(25	)		(b)			(27	)
Total realized and unrealized gains (losses)		(2	)		(25	)		(b)			(27	)
Purchases		—			—			1			1
Settlements		1			15			(1	)		15
Transfers out of Level 3		15			170			—			185
Ending balance at December 31, 2012	$	—		$	—		$	—		$	—
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2012	$	—		$	—		$	—		$	—
Power:
Beginning balance at January 1, 2012	$	21		$	(140	)	$	234		$	115
Realized and unrealized gains (losses):
Included in earnings(c)		—			—			27			27
Included in OCI		—			—			26			26
Included in regulatory assets/liabilities		11			(226	)		40			(175	)
Total realized and unrealized gains (losses)		11			(226	)		93			(122	)
Purchases		21			—			8			29
Sales		(1	)		—			2			1
Settlements		(37	)		255			(279	)		(61	)
Transfers out of Level 3		(4	)		—			1			(3	)
Ending balance at December 31, 2012	$	11		$	(111	)	$	59		$	(41	)
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2012	$	—		$	(191	)	(d) $	44		$	(147	)
Uranium:
Beginning balance at January 1, 2012	$	(1	)	$	(b)		$	(b)		$	(1	)
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		(2	)		(b)			(b)			(2	)
Total realized and unrealized gains (losses)		(2	)		(b)			(b)			(2	)
Settlements		1			(b)			(b)			1
Ending balance at December 31, 2012	$	(2	)	$	(b)		$	(b)		$	(2	)
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2012	$	(1	)	$	(b)		$	(b)		$	(1	)

(a) Includes amounts for Marketing Company, AERG, Genco, and intercompany eliminations, including the elimination of financial power contracts between Ameren Illinois and Marketing Company.

(b) Not applicable.

(c) Net gains and losses on power derivative commodity contracts are recorded in “Operating Revenues - Electric”.

(d) The change in unrealized losses was due to decreases in long-term power prices applied to 20-year Ameren Illinois swap contracts, which expire in May 2032.

The following table summarizes the changes in the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy as of December 31, 2011:

		Net Derivative Commodity Contracts
		Ameren Missouri			Ameren Illinois			Other(a)			Ameren
Fuel oils:
Beginning balance at January 1, 2011	$	30		$	(b)		$	21		$	51
Realized and unrealized gains (losses):
Included in earnings(c)		—			(b)			16			16
Included in regulatory assets/liabilities		19			(b)			(b)			19
Total realized and unrealized gains (losses)		19			(b)			16			35
Purchases		4			(b)			1			5
Sales		(1	)		(b)			—			(1	)
Settlements		(30	)		(b)			(26	)		(56	)
Transfers out of Level 3		(19	)		(b)			(11	)		(30	)
Ending balance at December 31, 2011	$	3		$	(b)		$	1		$	4
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2011	$	(11	)	$	(b)		$	(7	)	$	(18	)
Natural gas:
Beginning balance at January 1, 2011	$	(14	)	$	(134	)	$	—		$	(148	)
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		(8	)		(107	)		(b)			(115	)
Total realized and unrealized gains (losses)		(8	)		(107	)		(b)			(115	)
Purchases		—			1			—			1
Sales		—			(1	)		—			(1	)
Settlements		8			81			—			89
Ending balance at December 31, 2011	$	(14	)	$	(160	)	$	—		$	(174	)
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2011	$	(6	)	$	(72	)	$	—		$	(78	)
Power:
Beginning balance at January 1, 2011	$	2		$	(352	)	$	386		$	36
Realized and unrealized gains (losses):
Included in earnings(c)		—			—			(13	)		(13	)
Included in OCI		—			—			24			24
Included in regulatory assets/liabilities		17			7			51			75
Total realized and unrealized gains (losses)		17			7			62			86
Purchases		30			—			35			65
Sales		(1	)		—			(21	)		(22	)
Settlements		(27	)		205			(227	)		(49	)
Transfers into Level 3		(1	)		—			1			—
Transfers out of Level 3		1			—			(2	)		(1	)
Ending balance at December 31, 2011	$	21		$	(140	)	$	234		$	115
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2011	$	1		$	13		$	59		$	73
Uranium:
Beginning balance at January 1, 2011	$	2		$	(b)		$	(b)		$	2
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		(3	)		(b)			(b)			(3	)
Total realized and unrealized gains (losses)		(3	)		(b)			(b)			(3	)
Purchases		(1	)		(b)			(b)			(1	)
Settlements		1			(b)			(b)			1
Ending balance at December 31, 2011	$	(1	)	$	(b)		$	(b)		$	(1	)
Change in unrealized gains (losses) related to assets/liabilities held at December 31, 2011	$	—		$	(b)		$	(b)		$	—

(a) Includes amounts for Marketing Company, AERG, Genco, and intercompany eliminations, including the elimination of financial power contracts between Ameren Illinois and Marketing Company.

(b) Not applicable.

(c) Net gains and losses on fuel oils derivative commodity contracts are recorded in "Operating Expenses - Fuel," while net gains and losses on power derivative commodity contracts are recorded in “Operating Revenues - Electric."

Schedule Of Transfers Between Fair Value Hierarchy Levels

The following table summarizes all transfers between fair value hierarchy levels related to derivative commodity contracts for the years ended December 31, 2012 and 2011:

	2012			2011
Ameren - derivative commodity contracts:(a)
Transfers into Level 3 / Transfers out of Level 1 - Fuel oils	$	2		$	—
Transfers out of Level 3 / Transfers into Level 1 - Fuel oils	(1		)	(30		)
Transfers out of Level 3 / Transfers into Level 2 - Natural gas	185			—
Transfers into Level 3 / Transfers out of Level 2 - Power	—			—
Transfers out of Level 3 / Transfers into Level 2 - Power	(3		)	(1		)
Net fair value of Level 3 transfers	$	183		$	(31	)
Ameren Missouri - derivative commodity contracts:
Transfers into Level 3 / Transfers out of Level 1 - Fuel oils	$	1		$	—
Transfers out of Level 3 / Transfers into Level 1 - Fuel oils	—			(19		)
Transfers out of Level 3 / Transfers into Level 2 - Natural gas	15			—
Transfers into Level 3 / Transfers out of Level 2 - Power	—			(1		)
Transfers out of Level 3 / Transfers into Level 2 - Power	(4		)	1
Net fair value of Level 3 transfers	$	12		$	(19	)
Ameren Illinois - derivative commodity contracts:
Transfers out of Level 3 / Transfers into Level 2 - Natural gas	$	170		$	—

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

Schedule Of Carrying Amounts And Estimated Fair Values Of Long-Term Debt And Preferred Stock

The following table presents the carrying amounts and estimated fair values of our long-term debt and preferred stock at December 31, 2012 and 2011:

	2012				2011
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Ameren:(a)(b)
Long-term debt and capital lease obligations (including current portion)	$	6,981	$	7,728	$	6,856	$	7,800
Preferred stock	142		123		142		92
Ameren Missouri:
Long-term debt and capital lease obligations (including current portion)	$	4,006	$	4,625	$	3,950	$	4,541
Preferred stock	80		73		80		55
Ameren Illinois:
Long-term debt (including current portion)	$	1,727	$	2,020	$	1,658	$	1,943
Preferred stock	62		49		62		37
Genco:
Long-term debt (including current portion)	$	824	$	618	$	824	$	839

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

(b) Preferred stock along with the noncontrolling interest of EEI is recorded in "Noncontrolling Interests" on the balance sheet.