Fair Value (Fair Value Of Financial Assets And Liabilities Measured On A Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Assets
Available-for-sale, securities	$ 154.9	$ 151.6
Total	194.5	236.4
Liabilities
Total	4.2	3.0
Fair Value, Inputs, Level 1
Assets
Risk management assets	0.0	0.0
Available-for-sale, securities	0.0	0.0
Total	0.0	0.0
Liabilities
Risk management liabilities	0.0	0.0
Total	0.0	0.0
Significant Other Observable Inputs (Level 2)
Assets
Risk management assets	39.6	84.8
Available-for-sale, securities	154.9	151.6
Total	194.5	236.4
Liabilities
Risk management liabilities	4.2	3.0
Total	4.2	3.0
Significant Unobservable Inputs (Level 3)
Assets
Risk management assets	0.0	0.0
Available-for-sale, securities	0.0	0.0
Total	0.0	0.0
Liabilities
Risk management liabilities	0.0	0.0
Total	0.0	0.0
Available-for-sale Securities
Assets
Available-for-sale, securities	154.9	151.6
Risk management assets
Assets
Risk management assets	39.6	84.8
Liabilities
Risk management liabilities	$ 4.2	$ 3.0