Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Aug. 16, 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%	(1.00%)	0.00%	0.00%
Amortization of excess deferred taxes	(8.00%)	(8.00%)	(8.00%)	(9.00%)
Depreciation differences	0.00%	0.00%
Renewable and other tax credits	(4.00%)	(2.00%)	(4.00%)	(3.00%)
State tax	4.00%	4.00%	5.00%	5.00%
Stock-based compensation	1.00%	0.00%	0.00%	(1.00%)
Cash surrender value of COLI	1.00%	0.00%
Effective income tax rate	15.00%	14.00%	14.00%	13.00%
Production and Investment Tax Credit Adder					10.00%
Greenhouse Emissions Reduction Target, Inflation Reduction Act					75.00%
Tax Credit Transferability, Inflation Reduction Act, Percent					100.00%
Minimum Tax on Book Income, Percent					15.00%
Minimum Adjusted Financial Statement Income Subject to Inflation Reduction Act Tax					$ 1,000
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%)	0.00%
Amortization of excess deferred taxes	(15.00%)	(17.00%)	(15.00%)	(17.00%)
Depreciation differences	0.00%	0.00%
Renewable and other tax credits	(10.00%)	(8.00%)	(10.00%)	(8.00%)
State tax	3.00%	4.00%	3.00%	3.00%
Stock-based compensation	0.00%	0.00%	0.00%	0.00%
Cash surrender value of COLI	0.00%	0.00%
Effective income tax rate	(2.00%)	(1.00%)	(2.00%)	(1.00%)
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%)	(3.00%)
Depreciation differences	0.00%	(1.00%)
Renewable and other tax credits	0.00%	0.00%	0.00%	0.00%
State tax	7.00%	7.00%	7.00%	7.00%
Stock-based compensation	0.00%	0.00%	0.00%	0.00%
Cash surrender value of COLI	0.00%	0.00%
Effective income tax rate	26.00%	25.00%	26.00%	25.00%