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, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Nuclear Waste Matters [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	$ 320
Total cash, cash equivalents, and restricted cash	155	$ 301	$ 176	$ 107
Fair Value	1,159	982
Cash and cash equivalents	8	139
Union Electric Company
Nuclear Waste Matters [Line Items]
Debt, Equity, Marketable, And Other Securities, Available-For-Sale, Amortized Cost	515	475
Total cash, cash equivalents, and restricted cash	8	145	$ 39	$ 8
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	650	516
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	6	9
Fair Value	1,159	982
Cash and cash equivalents	0	136
Debt, Equity, Marketable, And Other Securities, Available-For-Sale	1,159	982
Union Electric Company | Debt securities
Nuclear Waste Matters [Line Items]
Debt Securities, Available-for-sale, Amortized Cost	320	272
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	10	25
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2	0
Fair Value	328	297
Union Electric Company | Equity securities
Nuclear Waste Matters [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis	188	198
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	640	491
Available-for-sale Equity Securities, Accumulated Gross Unrealized Loss, before Tax	4	9
Equity Securities, FV-NI	824	680
Union Electric Company | Cash and cash equivalents
Nuclear Waste Matters [Line Items]
Marketable Securities	4	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	4	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	1
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	$ 1