Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Amortized Cost
Trading equity securities, amortized cost	$ 6.4	$ 4.7
Trading debt securities, amortized cost	10.8	12.7
Total trading equity and debt securities, amortized cost	17.2	17.4
Gross Unrealized Gains and Losses
Trading equity securities, gross unrealized gains	0.6	0.3
Trading debt securities, gross unrealized gains	0.3	0.1
Total trading equity and debt securities, gross unrealized gains	0.9	0.4
Trading equity securities, gross unrealized losses	0.0	0.1
Trading debt securities, gross unrealized losses	0.1	0.1
Total trading equity and debt securities, gross unrealized losses	0.1	0.2
Fair Value (Net Carrying Amount)
Trading equity securities, fair value (net carrying value)	7.0	4.9
Trading debt securities, fair value (net carrying value)	11.0	12.7
Total trading equity and debt securities, fair value (net carrying value)	$ 18.0	$ 17.6