Other Income, Net (Other Income And Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	$ 28	$ 36	$ 24
Interest income on industrial development revenue bonds	25	26	26
Interest and dividend income	8	7	8
Non-service cost components of net periodic benefit income	90	70	44
Other	6	8	5
Charitable donations	(12)	(33)	(8)
Other expense	(15)	(12)	(13)
Total other income, net	130	102	86
Union Electric Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	19	27	21
Interest income on industrial development revenue bonds	25	26	26
Interest and dividend income	1	2	1
Non-service cost components of net periodic benefit income	18	17	22
Other	5	4	3
Charitable donations	(3)	(14)	(2)
Other expense	(7)	(6)	(6)
Total other income, net	58	56	65
Defined Benefit Plan, Non-service Cost or Income Components - Tracker	29	17
Ameren Illinois Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	9	9	3
Interest and dividend income	6	6	7
Non-service cost components of net periodic benefit income	47	34	10
Other	3	3	2
Charitable donations	(5)	(6)	(5)
Other expense	(7)	(4)	(5)
Total other income, net	$ 53	$ 42	$ 12