Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21.00%	21.00%	21.00%	21.00%
Increases (decreases) from:
Amortization of deferred investment tax credit	0.00%	0.00%	0.00%	0.00%
Amortization of excess deferred taxes	(7.00%)	(8.00%)	(8.00%)	(8.00%)
Depreciation differences	(1.00%)	0.00%	0.00%	0.00%
Renewable and other tax credits	(5.00%)	(4.00%)	(5.00%)	(4.00%)
State tax	4.00%	4.00%	5.00%	5.00%
Stock-based compensation	0.00%	1.00%
Cash surrender value of COLI	0.00%	1.00%
Effective income tax rate	12.00%	15.00%	13.00%	14.00%
Union Electric Company
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21.00%	21.00%	21.00%	21.00%
Increases (decreases) from:
Amortization of deferred investment tax credit	(1.00%)	(1.00%)	(1.00%)	(1.00%)
Amortization of excess deferred taxes	(15.00%)	(15.00%)	(15.00%)	(15.00%)
Depreciation differences	0.00%	0.00%	0.00%	0.00%
Renewable and other tax credits	(11.00%)	(10.00%)	(11.00%)	(10.00%)
State tax	3.00%	3.00%	3.00%	3.00%
Stock-based compensation	0.00%	0.00%
Cash surrender value of COLI	0.00%	0.00%
Effective income tax rate	(3.00%)	(2.00%)	(3.00%)	(2.00%)
Ameren Illinois Company
Income Taxes [Line Items]
Federal statutory corporate income tax rate	21.00%	21.00%	21.00%	21.00%
Increases (decreases) from:
Amortization of deferred investment tax credit	0.00%	0.00%	0.00%	0.00%
Amortization of excess deferred taxes	(2.00%)	(2.00%)	(2.00%)	(2.00%)
Depreciation differences	0.00%	0.00%	(1.00%)	0.00%
Renewable and other tax credits	(1.00%)	0.00%	0.00%	0.00%
State tax	7.00%	7.00%	7.00%	7.00%
Stock-based compensation	0.00%	0.00%
Cash surrender value of COLI	0.00%	0.00%
Effective income tax rate	25.00%	26.00%	25.00%	26.00%