Callaway Energy Center (Fair Values Of Investments In Debt And Equity Securities In Nuclear Decommissioning Trust Fund) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Nuclear Waste Matters [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 374
Total cash, cash equivalents, and restricted cash	216	$ 155	$ 301	$ 176
Fair Value	958	1,159
Cash and cash equivalents	10	8
Union Electric Company
Nuclear Waste Matters [Line Items]
Debt, Equity, Marketable, And Other Securities, Available-For-Sale, Amortized Cost	562	515
Total cash, cash equivalents, and restricted cash	13	8	$ 145	$ 39
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	455	650
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	59	6
Fair Value	958	1,159
Cash and cash equivalents	0	0
Debt, Equity, Marketable, And Other Securities, Available-For-Sale	958	1,159
Union Electric Company | Debt securities
Nuclear Waste Matters [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	374	320
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0	10
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	45	2
Fair Value	329	328
Union Electric Company | Equity securities
Nuclear Waste Matters [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis	177	188
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	455	640
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax	14	4
Equity Securities, FV-NI	618	824
Union Electric Company | Cash and cash equivalents
Nuclear Waste Matters [Line Items]
Marketable Securities	8	4
Total cash, cash equivalents, and restricted cash	0	0
Cash and Cash Equivalents and Restricted Cash and Cash Equivalents	0	0
Cash and cash equivalents	8	4
Union Electric Company | Other Debt And Equity Securities
Nuclear Waste Matters [Line Items]
Net Receivables (Payables) From Pending Securities Sales, Interest, and Securities Purchases, Cost Basis	3	3
Net Receivables (Payables) From Pending Securities Sales, Interest, And Securities Purchases, Available-For-sale Securities, Accumulated Gross Unrealized Gain, Before Tax	0	0
Net Receivables (Payables) From Pending Securities Sales, Interest, And Securities Purchases, Available-For-sale Securities, Accumulated Gross Unrealized Loss, Before Tax	0	0
Net Receivables (Payables) From Pending Securities Sales, Interest, and Securities Purchases, Fair Value	$ 3	$ 3