Callaway Energy Center (Proceeds From The Sale Of Investments And Related Gross Realized Gains And Losses In Nuclear Decommissioning Trust Fund) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Nuclear Waste Matters [Line Items]
Sales and maturities of securities - nuclear decommissioning trust fund	$ 299	$ 305	$ 304
Gross realized gains	18	13	7
Gross realized losses	5	5	4
Union Electric Company
Nuclear Waste Matters [Line Items]
Sales and maturities of securities - nuclear decommissioning trust fund	$ 299	$ 305	$ 304
Minimum | Nuclear Decommissioning Trust Fund [Member]
Nuclear Waste Matters [Line Items]
Trust fund investments, target allocation percentage	60.00%
Maximum | Nuclear Decommissioning Trust Fund [Member]
Nuclear Waste Matters [Line Items]
Trust fund investments, target allocation percentage	70.00%