Callaway Energy Center (Cost and Fair Values of Investments In Debt Securities in Nuclear Decommissioning Trust Fund According to Contractual Maturities) (Details) $ in Millions	Dec. 31, 2023 USD ($)
Nuclear Waste Matters [Abstract]
Cost, Less than 5 years	$ 101
Cost, 5 years to 10 years	163
Cost, Due after 10 years	118
Cost, Total	382
Fair Value, Less than 5 years	98
Fair Value, 5 years to 10 years	156
Fair Value, Due after 10 years	100
Fair Value, Total	$ 354