Derivative Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2014

Derivative Instrument Detail [Abstract]

Open Gross Derivative Volumes By Commodity Type

The following table presents open gross commodity contract volumes by commodity type for derivative assets and liabilities as of December 31, 2014 and 2013. As of December 31, 2014, these contracts ran through October 2017, October 2019, May 2032, and October 2016 for fuel oils, natural gas, power, and uranium, respectively.

	Quantity (in millions, except as indicated)
	2014			2013
Commodity	Ameren Missouri	Ameren Illinois	Ameren	Ameren Missouri	Ameren Illinois	Ameren
Fuel oils (in gallons)(a)	50	(b)	50	66	(b)	66
Natural gas (in mmbtu)	28	108	136	28	108	136
Power (in megawatthours)	1	11	12	3	11	14
Uranium (pounds in thousands)	332	(b)	332	796	(b)	796

(a) Fuel oils consist of heating oil, ultra-low-sulfur diesel, and crude oil.

(b) Not applicable.

Derivative Instruments Carrying Value

The following table presents the carrying value and balance sheet location of all derivative commodity contracts, none of which were designated as hedging instruments, as of December 31, 2014 and 2013:

	Balance Sheet Location		Ameren Missouri		Ameren Illinois		Ameren
2014
Fuel oils	Other current assets	$	2	$	—	$	2
Natural gas	Other current assets		1		1		2
Power	Other current assets		15		—		15
	Total assets	$	18	$	1	$	19
Fuel oils	Other current liabilities	$	22	$	—	$	22
	Other deferred credits and liabilities		7		—		7
Natural gas	MTM derivative liabilities		(a)		31		(a)
	Other current liabilities		6		—		37
	Other deferred credits and liabilities		6		13		19
Power	MTM derivative liabilities		(a)		11		(a)
	Other current liabilities		3		—		14
	Other deferred credits and liabilities		—		131		131
Uranium	Other current liabilities		2		—		2
	Total liabilities	$	46	$	186	$	232
2013
Fuel oils	Other current assets	$	6	$	—	$	6
	Other assets		3		—		3
Natural gas	Other current assets		1		1		2
Power	Other current assets		23		—		23
	Total assets	$	33	$	1	$	34
Fuel oils	Other current liabilities	$	2	$	—	$	2
	Other deferred credits and liabilities		1		—		1
Natural gas	MTM derivative liabilities		(a)		27		(a)
	Other current liabilities		5		—		32
	Other deferred credits and liabilities		6		19		25
Power	MTM derivative liabilities		(a)		9		(a)
	Other current liabilities		4		—		13
	Other deferred credits and liabilities		—		99		99
Uranium	Other current liabilities		5		—		5
	Other deferred credits and liabilities		1		—		1
	Total liabilities	$	24	$	154	$	178

(a) Balance sheet line item not applicable to registrant.

Cumulative Pretax Net Gains (Losses) On All Derivative Instruments In OCI

The following table presents the cumulative amount of pretax net gains (losses) on all derivative instruments deferred in regulatory assets or regulatory liabilities as of December 31, 2014 and 2013:

		Ameren Missouri			Ameren Illinois			Ameren
2014
Fuel oils derivative contracts(a)	$	(29	)	$	—		$	(29	)
Natural gas derivative contracts(b)		(11	)		(43	)		(54	)
Power derivative contracts(c)		12			(142	)		(130	)
Uranium derivative contracts(d)		(2	)		—			(2	)
2013
Fuel oils derivative contracts	$	2		$	—		$	2
Natural gas derivative contracts		(10	)		(45	)		(55	)
Power derivative contracts		19			(108	)		(89	)
Uranium derivative contracts		(6	)		—			(6	)

(a) Represents net losses associated with fuel oils derivative contracts at Ameren Missouri. These contracts are a partial hedge of Ameren Missouri’s rail transportation surcharges for coal through December 2017. Current losses deferred as regulatory assets include $21 million and $21 million at Ameren and Ameren Missouri, respectively.

(b) Represents net losses associated with natural gas derivative contracts. These contracts are a partial hedge of natural gas requirements through October 2019 at Ameren and Ameren Missouri and through October 2018 at Ameren Illinois. Current gains deferred as regulatory liabilities include $2 million, $1 million, and $1 million at Ameren, Ameren Missouri, and Ameren Illinois, respectively. Current losses deferred as regulatory assets include $37 million, $6 million, and $31 million at Ameren, Ameren Missouri, and Ameren Illinois, respectively.

(c) Represents net gains (losses) associated with power derivative contracts. These contracts are a partial hedge of power price requirements through May 2032 at Ameren and Ameren Illinois and through December 2015 at Ameren Missouri. Current gains deferred as regulatory liabilities include $15 million and $15 million at Ameren and Ameren Missouri, respectively. Current losses deferred as regulatory assets include $14 million, $3 million, and $11 million at Ameren, Ameren Missouri, and Ameren Illinois, respectively.

(d) Represents net losses associated with uranium derivative contracts at Ameren Missouri. These contracts are a partial hedge of Ameren Missouri's uranium requirements through December 2016. Current losses deferred as regulatory assets include $2 million and $2 million at Ameren and Ameren Missouri, respectively.

Derivative Instruments With Credit Risk-Related Contingent Features

The following table presents, as of December 31, 2014, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a gross liability position, the cash collateral posted, and the aggregate amount of additional collateral that could be required to be posted with counterparties. The additional collateral required is the net liability position allowed under the master netting arrangements assuming (1) the credit risk-related contingent features underlying these arrangements were triggered on December 31, 2014, and (2) those counterparties with rights to do so requested collateral.

	Aggregate Fair Value of Derivative Liabilities(a)		Cash Collateral Posted		Potential Aggregate Amount of Additional Collateral Required(b)
Ameren Missouri	$	96	$	4	$	88
Ameren Illinois	74		—		71
Ameren	$	170	$	4	$	159

(a) Prior to consideration of master netting arrangements and including NPNS and other accrual contract exposures.

(b) As collateral requirements with certain counterparties are based on master netting arrangements, the aggregate amount of additional collateral required to be posted is determined after consideration of the effects of such arrangements.

Offsetting Derivative Assets and Liabilities [Table Text Block]

The following table provides the recognized gross derivative balances and the net amounts of those derivatives subject to an enforceable master netting arrangement or similar agreement as of December 31, 2014 and 2013:

				Gross Amounts Not Offset on the Balance Sheet
Commodity Contracts Eligible to be Offset		Gross Amounts Recognized on the Balance Sheet		Derivative Instruments		Cash Collateral Received/Posted(a)		Net Amount
2014
Assets:
Ameren Missouri	$	18	$	5	$	—	$	13
Ameren Illinois		1		—		—		1
Ameren	$	19	$	5	$	—	$	14
Liabilities:
Ameren Missouri	$	46	$	5	$	5	$	36
Ameren Illinois		186		—		—		186
Ameren	$	232	$	5	$	5	$	222
2013
Assets:
Ameren Missouri	$	33	$	9	$	—	$	24
Ameren Illinois		1		1		—		—
Ameren	$	34	$	10	$	—	$	24
Liabilities:
Ameren Missouri	$	24	$	9	$	9	$	6
Ameren Illinois		154		1		15		138
Ameren	$	178	$	10	$	24	$	144

(a) Cash collateral received reduces gross asset balances and is included in “Other current liabilities” and “Other deferred credits and liabilities” on the balance sheet. Cash collateral posted reduces gross liability balances and is included in “Other current assets” and “Other assets” on the balance sheet.