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, 2021 USD ($)
Nuclear Waste Matters [Abstract]
Cost, Less than 5 years	$ 155
Cost, 5 years to 10 years	71
Cost, Due after 10 years	94
Cost, Total	320
Fair Value, Less than 5 years	156
Fair Value, 5 years to 10 years	72
Fair Value, Due after 10 years	100
Fair Value, Total	$ 328