Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2013

Fair Value Disclosures [Abstract]

Fair Value, Assets and Liabilities Measured on Nonrecurring Basis, Valuation Techniques [Table Text Block]

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 three months ended March 31, 2013:

		Fair Value								Weighted
		Assets		Liabilities			Valuation Technique(s)	Unobservable Input	Range	Average
Level 3 Derivative asset and liability - commodity contracts(a):
Ameren	Fuel oils	$	7	$	(2	)	Discounted cash flow	Escalation rate(%)(b)	.20 - .59	.39
								Counterparty credit risk(%)(c)(d)	.26 - 3	1
							Option model	Volatilities(%)(b)	10 - 19	17
	Natural gas	3		(1		)	Option model	Escalation rate(%)(b)	.20 - .46	.37
								Nodal basis($/mmbtu)(c)	(.24) - (.04)	(.19)
							Discounted cash flow	Escalation rate(%)(b)	.20 - .46	.35
								Nodal basis($/mmbtu)(c)	(.18) - 0	(.01)
								Counterparty credit risk(%)(c)(d)	.26 - 5	1
								Ameren credit risk(%)(c)(d)	2 - 3	3
	Power(e)	12		(91		)	Discounted cash flow	Average bid/ask consensus peak and off-peak pricing - forwards/swaps($/MWh)(c)	24 - 48	33
								Estimated auction price for FTRs($/MW)(b)	0 - 4,280	190
								Nodal basis($/MWh)(c)	(5) - (1)	(3)
								Counterparty credit risk(%)(c)(d)	.22 - 5	2
								Ameren credit risk(%)(c)(d)	2 - 3	3
							Fundamental energy production model	Estimated future gas prices($/mmbtu)(b)	5 - 7	6
							Contract price allocation	Estimated renewable energy credit costs($/credit)(d)	5 - 7	6
	Uranium	—		(2		)	Discounted cash flow	Average bid/ask consensus pricing($/pound)(b)	42 - 45	43
Ameren Missouri	Fuel oils	$	7	$	(2	)	Discounted cash flow	Escalation rate(%)(b)	.20 - .59	.39
								Counterparty credit risk(%)(c)(d)	.26 - 3	1
							Option model	Volatilities(%)(b)	10 - 19	17
	Natural gas	1		(1		)	Option model	Escalation rate(%)(b)	.20 - .46	.37
								Nodal basis($/mmbtu)(c)	(.24) - (.04)	(.19)
							Discounted cash flow	Escalation rate(%)(b)	.20 - .46	.26
								Nodal basis($/mmbtu)(c)	(.18) - (.02)	(.04)
								Counterparty credit risk(%)(c)(d)	.26 - 5	1
								Ameren Missouri credit risk(%)(c)(d)	2	(f)
	Power(e)	9		(7		)	Discounted cash flow	Average bid/ask consensus peak and off-peak pricing - forwards/swaps($/MWh)(c)	24 - 51	38
								Estimated auction price for FTRs($/MW)(b)	0 - 4,280	190
								Nodal basis($/MWh)(c)	(5) - (1)	(3)
								Counterparty credit risk(%)(c)(d)	.22 - 5	1
								Ameren Missouri credit risk(%)(c)(d)	2	(f)
	Uranium	—		(2		)	Discounted cash flow	Average bid/ask consensus pricing($/pound)(b)	42 - 45	43
Ameren Illinois	Natural gas	$	2	$	—		Discounted cash flow	Escalation rate(%)(b)	.20 - .46	.33
								Nodal basis($/mmbtu)(c)	(.05) - 0	—
								Counterparty credit risk(%)(c)(d)	.70 - 2	1
								Ameren Illinois credit risk(%)(c)(d)	3	(f)
	Power(e)	3		(84		)	Discounted cash flow	Average bid/ask consensus peak and off-peak pricing - forwards/swaps($/MWh)(b)	24 - 42	32
								Nodal basis($/MWh)(b)	(4) - (1)	(3)
								Counterparty credit risk(%)(c)(d)	2	(f)
								Ameren Illinois credit risk(%)(c)(d)	3	(f)
							Fundamental energy production model	Estimated future gas prices($/mmbtu)(b)	5 - 7	6
							Contract price allocation	Estimated renewable energy credit costs($/credit)(b)	5 - 7	6

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

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

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

(d) 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.

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

(f) Not applicable.

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 twelve-month period ended December 31, 2012:

		Fair Value								Weighted
		Assets		Liabilities			Valuation Technique(s)	Unobservable Input	Range	Average
Level 3 Derivative asset and liability - commodity contracts(a):
Ameren	Fuel oils	$	8	$	(3	)	Discounted cash flow	Escalation rate(%)(b)	.21 - .60	.44
								Counterparty credit risk(%)(c)(d)	.12 - 1	1
								Ameren credit risk(%)(c)(d)	2	(e)
							Option model	Volatilities(%)(b)	7 - 27	24
	Power(f)	14		(114		)	Discounted cash flow	Average bid/ask consensus peak and off-peak pricing - forwards/swaps($/MWh)(c)	22 - 47	31
								Estimated auction price for FTRs($/MW)(b)	(281) - 1,851	178
								Nodal basis($/MWh)(c)	(5) - (1)	(3)
								Counterparty credit risk(%)(c)(d)	.22 - 1	1
								Ameren credit risk(%)(c)(d)	2 - 5	5
							Fundamental energy production model	Estimated future gas prices($/mmbtu)(b)	4 - 8	6
							Contract price allocation	Estimated renewable energy credit costs($/credit)(b)	5 - 7	6
	Uranium	—		(2		)	Discounted cash flow	Average bid/ask consensus pricing($/pound)(b)	43 - 46	44
Ameren Missouri	Fuel oils	$	8	$	(3	)	Discounted cash flow	Escalation rate(%)(b)	.21 - .60	.44
								Counterparty credit risk(%)(c)(d)	.12 - 1	1
								Ameren Missouri credit risk(%)(c)(d)	2	(e)
							Option model	Volatilities(%)(b)	7 - 27	24
	Power(f)	14		(3		)	Discounted cash flow	Average bid/ask consensus peak and off-peak pricing - forwards/swaps($/MWh)(c)	24 - 56	36
								Estimated auction price for FTRs($/MW)(b)	(281) - 1,851	178
								Nodal basis($/MWh)(c)	(5) - (1)	(2)
								Counterparty credit risk(%)(c)(d)	.22 - 1	1
								Ameren Missouri credit risk(%)(c)(d)	2
	Uranium	—		(2		)	Discounted cash flow	Average bid/ask consensus pricing($/pound)(b)	43 - 46	44
Ameren Illinois	Power(f)	$	—	$	(111	)	Discounted cash flow	Average bid/ask consensus peak and off-peak pricing - forwards/swaps($/MWh)(b)	22 - 47	30
								Nodal basis($/MWh)(b)	(5) - (1)	(3)
								Ameren Illinois credit risk(%)(c)(d)	5	(e)
							Fundamental energy production model	Estimated future gas prices($/mmbtu)(b)	4 - 8	6
							Contract price allocation	Estimated renewable energy credit costs($/credit)(b)	5 - 7	6

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

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

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

(d) 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.

(e) Not applicable.

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

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 March 31, 2013:

		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	Derivative assets - commodity contracts(a):
	Fuel oils	$	3	$	—	$	7	$	10
	Natural gas	1		4		3		8
	Power	—		7		12		19
	Total derivative assets - commodity contracts	$	4	$	11	$	22	$	37
	Nuclear Decommissioning Trust Fund(b):
	Cash and cash equivalents	$	2	$	—	$	—	$	2
	Equity securities:
	U.S. large capitalization	294		—		—		294
	Debt securities:
	Corporate bonds	—		48		—		48
	Municipal bonds	—		1		—		1
	U.S. treasury and agency securities	—		77		—		77
	Asset-backed securities	—		11		—		11
	Other	—		1		—		1
	Total Nuclear Decommissioning Trust Fund	$	296	$	138	$	—	$	434
	Total Ameren	$	300	$	149	$	22	$	471
Ameren	Derivative assets - commodity contracts(a):
Missouri	Fuel oils	$	3	$	—	$	7	$	10
	Natural gas	—		1		1		2
	Power	—		7		9		16
	Total derivative assets - commodity contracts	$	3	$	8	$	17	$	28
	Nuclear Decommissioning Trust Fund(b):
	Cash and cash equivalents	$	2	$	—	$	—	$	2
	Equity securities:
	U.S. large capitalization	294		—		—		294
	Debt securities:
	Corporate bonds	—		48		—		48
	Municipal bonds	—		1		—		1
	U.S. treasury and agency securities	—		77		—		77
	Asset-backed securities	—		11		—		11
	Other	—		1		—		1
	Total Nuclear Decommissioning Trust Fund	$	296	$	138	$	—	$	434
	Total Ameren Missouri	$	299	$	146	$	17	$	462
Ameren	Derivative assets - commodity contracts(a):
Illinois	Natural gas	$	1	$	3	$	2	$	6
	Power	—		—		3		3
	Total Ameren Illinois	$	1	$	3	$	5	$	9
Liabilities:
Ameren	Derivative liabilities - commodity contracts(a):
	Fuel oils	$	1	$	—	$	2	$	3
	Natural gas	5		73		1		79
	Power	—		8		91		99
	Uranium	—		—		2		2
	Total Ameren	$	6	$	81	$	96	$	183
Ameren	Derivative liabilities - commodity contracts(a):
Missouri	Fuel oils	$	1	$	—	$	2	$	3
	Natural gas	5		6		1		12
	Power	—		8		7		15
	Uranium	—		—		2		2
	Total Ameren Missouri	$	6	$	14	$	12	$	32
Ameren	Derivative liabilities - commodity contracts(a):
Illinois	Natural gas	$	—	$	67	$	—	$	67
	Power	—		—		84		84
	Total Ameren Illinois	$	—	$	67	$	84	$	151

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

(b) Balance excludes $3 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, 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	Derivative assets - commodity contracts(a):
	Fuel oils	$	4	$	—	$	8	$	12
	Natural gas	—		2		—		2
	Power	—		1		14		15
	Total derivative assets - commodity contracts	$	4	$	3	$	22	$	29
	Nuclear Decommissioning Trust Fund(b):
	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	$	269	$	144	$	22	$	435
Ameren	Derivative assets - commodity contracts(a):
Missouri	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(b):
	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	Derivative assets - commodity contracts(a):
Illinois	Natural gas	$	—	$	1	$	—	$	1
	Power	—		—		—		—
	Total Ameren Illinois	$	—	$	1	$	—	$	1

		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
Liabilities:
Ameren	Derivative liabilities - commodity contracts(a):
	Fuel oils	$	1	$	—	$	3	$	4
	Natural gas	7		102		—		109
	Power	—		1		114		115
	Uranium	—		—		2		2
	Total Ameren	$	8	$	103	$	119	$	230
Ameren	Derivative liabilities - commodity contracts(a):
Missouri	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	Derivative liabilities - commodity contracts(a):
Illinois	Natural gas	$	—	$	94	$	—	$	94
	Power	—		—		111		111
	Total Ameren Illinois	$	—	$	94	$	111	$	205

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

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

Schedule Of Changes In The Fair Value Of Financial Assets And Liabilities Classified As Level Three 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 for the three months ended March 31, 2013:

		Net derivative commodity contracts
		Ameren Missouri			Ameren Illinois			Ameren
Fuel oils:
Beginning balance at January 1, 2013	$	5		$	(a)		$	5
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		—			(a)			—
Total realized and unrealized gains (losses)		—			(a)			—
Purchases		1			(a)			1
Sales		—			(a)			—
Settlements		(1	)		(a)			(1	)
Ending balance at March 31, 2013	$	5		$	(a)		$	5
Change in unrealized gains (losses) related to assets/liabilities held at March 31, 2013	$	—		$	(a)		$	—
Natural gas:
Beginning balance at January 1, 2013	$	—		$	—		$	—
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		—			1			1
Total realized and unrealized gains (losses)		—			1			1
Purchases		—			1			1
Ending balance at March 31, 2013	$	—		$	2		$	2
Change in unrealized gains (losses) related to assets/liabilities held at March 31, 2013	$	—		$	—		$	—
Power:
Beginning balance at January 1, 2013	$	11		$	(111	)	$	(100	)
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		5			14			19
Total realized and unrealized gains (losses)		5			14			19
Settlements		(13	)		16			3
Transfers into Level 3		(2	)		—			(2	)
Transfers out of Level 3		1			—			1
Ending balance at March 31, 2013	$	2		$	(81	)	$	(79	)
Change in unrealized gains (losses) related to assets/liabilities held at March 31, 2013	$	(3	)	$	14		$	11
Uranium:
Beginning balance at January 1, 2013	$	(2	)	$	(a)		$	(2	)
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		—			(a)			—
Total realized and unrealized gains (losses)		—			(a)			—
Ending balance at March 31, 2013	$	(2	)	$	(a)		$	(2	)
Change in unrealized gains (losses) related to assets/liabilities held at March 31, 2013	$	—		$	(a)		$	—

(a) Not applicable.

The following table summarizes the changes in the fair value of financial assets and liabilities classified as Level 3 in the fair value hierarchy for the three months ended March 31, 2012:

		Net derivative commodity contracts
		Ameren Missouri				Ameren Illinois			Ameren
Fuel oils:
Beginning balance at January 1, 2012	$	3			$	(a)		$	3
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		2				(a)			2
Total realized and unrealized gains (losses)		2				(a)			2
Transfers into Level 3		2				(a)			2
Ending balance at March 31, 2012	$	7			$	(a)		$	7
Change in unrealized gains (losses) related to assets/liabilities held at March 31, 2012	$	2			$	(a)		$	2
Natural gas:
Beginning balance at January 1, 2012	$	(14		)	$	(160	)	$	(174		)
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		(2		)		(26	)		(28		)
Total realized and unrealized gains (losses)		(2		)		(26	)		(28		)
Settlements		1				16			17
Transfers out of Level 3		15				170			185
Ending balance at March 31, 2012	$	—			$	—		$	—
Change in unrealized gains (losses) related to assets/liabilities held at March 31, 2012	$	—			$	—		$	—
Power(b):
Beginning balance at January 1, 2012	$	21			$	(140	)	$	81
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		13				(220	)		(158		)
Total realized and unrealized gains (losses)		13				(220	)		(158		)
Settlements		(13		)		76			(4		)
Transfers out of Level 3		(1		)		—			(1		)
Ending balance at March 31, 2012	$	20			$	(284	)	$	(82		)
Change in unrealized gains (losses) related to assets/liabilities held at March 31, 2012	$	10			$	(202	)	(c) $	(156		)
Uranium:
Beginning balance at January 1, 2012		$	(1	)		(a)			$	(1	)
Realized and unrealized gains (losses):
Included in regulatory assets/liabilities		—				(a)			—
Total realized and unrealized gains (losses)		—				(a)			—
Ending balance at March 31, 2012		$	(1	)		(a)			$	(1	)
Change in unrealized gains (losses) related to assets/liabilities held at March 31, 2012		$	—			(a)			$	—

(a) Not applicable.

(b) Ameren amounts include the elimination of financial power contracts between Ameren Illinois and Marketing Company.

(c) 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.

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 three months ended March 31, 2013, and 2012:

	2013			2012
Ameren - derivative commodity contracts:
Transfers into Level 3 / Transfers out of Level 1 - Fuel oils	$	—		$	2
Transfers out of Level 3 / Transfers into Level 2 - Natural gas	—			185
Transfers into Level 3 / Transfers out of Level 2 - Power	(2		)	—
Transfers out of Level 3 / Transfers into Level 2 - Power	1			(1		)
Net fair value of Level 3 transfers	$	(1	)	$	186
Ameren Missouri - derivative commodity contracts:
Transfers into Level 3 / Transfers out of Level 1 - Fuel oils	$	—		$	2
Transfers out of Level 3 / Transfers into Level 2 - Natural gas	—			15
Transfers into Level 3 / Transfers out of Level 2 - Power	(2		)	—
Transfers out of Level 3 / Transfers into Level 2 - Power	1			(1		)
Net fair value of Level 3 transfers	$	(1	)	$	16
Ameren Illinois - derivative commodity contracts:
Transfers out of Level 3 / Transfers into Level 2 - Natural gas	$	—		$	170

Schedule Of Carrying Amounts And Estimated Fair Values Of Long-Term Debt, Capital Lease Obligations And Preferred Stock

The following table presents the carrying amounts and estimated fair values of our long-term debt and capital lease obligations and preferred stock at March 31, 2013, and December 31, 2012:

	March 31, 2013				December 31, 2012
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Ameren:(a)(b)
Long-term debt and capital lease obligations (including current portion)	$	6,158	$	7,127	$	6,157	$	7,110
Preferred stock	142		124		142		123
Ameren Missouri:
Long-term debt and capital lease obligations (including current portion)	$	4,006	$	4,645	$	4,006	$	4,625
Preferred stock	80		74		80		73
Ameren Illinois:
Long-term debt (including current portion)	$	1,727	$	2,027	$	1,727	$	2,020
Preferred stock	62		50		62		49

(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.