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, 2018 USD ($)
Nuclear Waste Matters [Abstract]
Cost, Less than 5 years	$ 140
Cost, 5 years to 10 years	48
Cost, Due after 10 years	65
Cost, Total	253
Fair Value, Less than 5 years	140
Fair Value, 5 years to 10 years	47
Fair Value, Due after 10 years	65
Fair Value, Total	$ 252