Derivative Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2019

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, 2019 and 2018. As of December 31, 2019, these contracts extended through October 2022, March 2024, May 2032, and March 2023 for fuel oils, natural gas, power, and uranium, respectively.

	Quantity (in millions, except as indicated)
	2019			2018
Commodity	Ameren Missouri	Ameren Illinois	Ameren	Ameren Missouri	Ameren Illinois	Ameren
Fuel oils (in gallons)	58	—	58	66	—	66
Natural gas (in mmbtu)	20	136	156	19	154	173
Power (in megawatthours)	5	7	12	1	8	9
Uranium (pounds in thousands)	565	—	565	380	—	380

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, 2019 and 2018:

			2019					2018
Commodity	Balance Sheet Location		Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois		Ameren
Fuel oils	Other current assets	$	4	$	—	$	4	$	3	$	—	$	3
	Other assets		2		—		2		5		—		5
Natural gas	Other current assets		—		3		3		—		1		1
	Other assets		—		1		1		—		2		2
Power	Other current assets		14		—		14		4		—		4
	Other assets		2		—		2		—		—		—
	Total assets	$	22	$	4	$	26	$	12	$	3	$	15
Fuel oils	Other current liabilities	$	4	$	—	$	4	$	4	$	—	$	4
	Other deferred credits and liabilities		3		—		3		9		—		9
Natural gas	Other current liabilities		1		12		13		4		8		12
	Other deferred credits and liabilities		1		6		7		1		6		7
Power	Other current liabilities		2		17		19		4		14		18
	Other deferred credits and liabilities		1		207		208		—		169		169
Uranium	Other deferred credits and liabilities		1		—		1		—		—		—
	Total liabilities	$	13	$	242	$	255	$	22	$	197	$	219