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Financial Instruments (Schedule of Investment Portfolio Activity) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]      
Proceeds from sales $ 174.7 $ 264.8 $ 431.6
Realized gross gains on sales 2.8 4.5 4.9
Realized gross losses on sales $ 1.7 $ 8.2 $ 3.0