Derivative Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2020

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, 2020 and 2019. As of December 31, 2020, these contracts extended through October 2023, March 2026, May 2032, and March 2023 for fuel oils, natural gas, power, and uranium, respectively.

	Quantity (in millions, except as indicated)
	2020			2019
Commodity	Ameren Missouri	Ameren Illinois	Ameren	Ameren Missouri	Ameren Illinois	Ameren
Fuel oils (in gallons)	43	—	43	58	—	58
Natural gas (in mmbtu)	33	114	147	20	136	156
Power (in MWhs)	6	7	13	5	7	12
Uranium (pounds in thousands)	365	—	365	565	—	565

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, 2020 and 2019:

			2020					2019
Commodity	Balance Sheet Location		Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois		Ameren
Fuel oils	Other current assets	$	2	$	—	$	2	$	4	$	—	$	4
	Other assets		—		—		—		2		—		2
Natural gas	Other current assets		1		8		9		—		3		3
	Other assets		2		2		4		—		1		1
Power	Other current assets		7		—		7		14		—		14
	Other assets		—		—		—		2		—		2
	Total assets	$	12	$	10	$	22	$	22	$	4	$	26
Fuel oils	Other current liabilities	$	7	$	—	$	7	$	4	$	—	$	4
	Other deferred credits and liabilities		2		—		2		3		—		3
Natural gas	Other current liabilities		1		1		2		1		12		13
	Other deferred credits and liabilities		—		1		1		1		6		7
Power	Other current liabilities		3		17		20		2		17		19
	Other deferred credits and liabilities		8		181		189		1		207		208
Uranium	Other deferred credits and liabilities		—		—		—		1		—		1
	Total liabilities	$	21	$	200	$	221	$	13	$	242	$	255