Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Taxes [Line Items]
Deferred Tax Liabilities, Net	$ 3,469	$ 3,177
Union Electric Company
Income Taxes [Line Items]
Deferred Tax Liabilities, Net	$ 1,822	$ 1,708
State | Union Electric Company
Income Taxes [Line Items]
State Income Tax Statutory Rate	4.00%
Deferred Tax Liabilities, Net	$ 122
State | Union Electric Company | Maximum
Income Taxes [Line Items]
State Income Tax Statutory Rate	6.25%