Other Income, Net (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	$ 8	$ 7
Interest income on industrial development revenue bonds	6	6
Non-service cost components of net periodic benefit income	46	34
Miscellaneous income	7	5
Donations	(2)	(3)
Miscellaneous expense	(5)	(3)
Total Other Income, Net	60	46
Union Electric Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	4	4
Interest income on industrial development revenue bonds	6	6
Non-service cost components of net periodic benefit income	14	14
Miscellaneous income	2	1
Donations	(1)	0
Miscellaneous expense	(2)	(2)
Total Other Income, Net	23	23
Defined Benefit Plan, Non-service Cost or Income Components - Tracker	6	(1)
Ameren Illinois Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	4	3
Non-service cost components of net periodic benefit income	21	14
Miscellaneous income	2	1
Donations	(1)	(3)
Miscellaneous expense	(2)	(1)
Total Other Income, Net	$ 24	$ 14