Other Income, Net (Other Income And Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	$ 32	$ 28	$ 36
Interest income on industrial development revenue bonds	25	25	26
Other interest income	4	8	7
Non-service cost components of net periodic benefit income	116	90	70
Miscellaneous income	13	6	8
Donations	(25)	(12)	(33)
Miscellaneous expense	(14)	(15)	(12)
Total other income, net	151	130	102
Union Electric Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	19	19	27
Interest income on industrial development revenue bonds	25	25	26
Other interest income	1	1	2
Non-service cost components of net periodic benefit income	46	18	17
Miscellaneous income	4	5	4
Donations	(12)	(3)	(14)
Miscellaneous expense	(7)	(7)	(6)
Total other income, net	76	58	56
Defined Benefit Plan, Non-service Cost or Income Components - Tracker	(4)	29	17
Union Electric Company | Final Rate Order | Electric
Other Nonoperating Income (Expense) [Line Items]
Donations	(8)
Ameren Illinois Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	13	9	9
Other interest income	3	6	6
Non-service cost components of net periodic benefit income	48	47	34
Miscellaneous income	6	3	3
Donations	(5)	(5)	(6)
Miscellaneous expense	(6)	(7)	(4)
Total other income, net	$ 59	$ 53	$ 42