Derivative Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2016

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, 2016 and 2015. As of December 31, 2016, these contracts extended through October 2019, March 2021, May 2032, and February 2020 for fuel oils, natural gas, power, and uranium, respectively.

	Quantity (in millions, except as indicated)
	2016			2015
Commodity	Ameren Missouri	Ameren Illinois	Ameren	Ameren Missouri	Ameren Illinois	Ameren
Fuel oils (in gallons)(a)	30	(b)	30	35	(b)	35
Natural gas (in mmbtu)	25	129	154	30	151	181
Power (in megawatthours)	1	9	10	1	10	11
Uranium (pounds in thousands)	345	(b)	345	494	(b)	494

(a) Consists of ultra-low-sulfur diesel products.

(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, 2016 and 2015:

	Balance Sheet Location		Ameren Missouri		Ameren Illinois		Ameren
2016
Fuel oils	Other current assets	$	2	$	—	$	2
	Other assets		1		—		1
Natural gas	Other current assets		1		11		12
	Other assets		1		2		3
Power	Other current assets		9		—		9
	Total assets (a)	$	14	$	13	$	27
Fuel oils	Other current liabilities	$	5	$	—	$	5
Natural gas	MTM derivative liabilities		(b)		3		(b)
	Other current liabilities		1		—		4
	Other deferred credits and liabilities		5		5		10
Power	MTM derivative liabilities		(b)		12		(b)
	Other current liabilities		3		—		15
	Other deferred credits and liabilities		—		173		173
Uranium	Other deferred credits and liabilities		4		—		4
	Total liabilities (c)	$	18	$	193	$	211
2015
Natural gas	Other current assets	$	—		1	$	1
	Other assets		1		—		1
Power	Other current assets		16		—		16
	Total assets (a)	$	17	$	1	$	18
Fuel oils	Other current liabilities	$	22	$	—	$	22
	Other deferred credits and liabilities		7		—		7
Natural gas	MTM derivative liabilities		(b)		32		(b)
	Other current liabilities		6		—		38
	Other deferred credits and liabilities		8		18		26
Power	MTM derivative liabilities		(b)		13		(b)
	Other current liabilities		—		—		13
	Other deferred credits and liabilities		—		157		157
Uranium	Other current liabilities		1		—		1
	Total liabilities (c)	$	44	$	220	$	264

(a) The cumulative amount of pretax net gains on all derivative instruments is deferred as a regulatory liability.

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

(c) The cumulative amount of pretax net losses on all derivative instruments is deferred as a regulatory asset.

Derivative Instruments With Credit Risk-Related Contingent Features

The following table presents, as of December 31, 2016, 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 counterparties could require. The additional collateral required is the net liability position allowed under the master netting arrangements or similar agreements, assuming (1) the credit risk-related contingent features underlying these arrangements were triggered on December 31, 2016, 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)
2016
Ameren Missouri	$	64	$	3	$	54
Ameren Illinois	33		—		26
Ameren	$	97	$	3	$	80

(a) Before consideration of master netting arrangements or similar agreements and including NPNS and other accrual contract exposures.

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