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, 2019 USD ($)
Nuclear Waste Matters [Abstract]
Cost, Less than 5 years	$ 112
Cost, 5 years to 10 years	56
Cost, Due after 10 years	94
Cost, Total	262
Fair Value, Less than 5 years	114
Fair Value, 5 years to 10 years	58
Fair Value, Due after 10 years	101
Fair Value, Total	$ 273