Restricted Securities Available for Sale (Schedule of Cost and Estimated Fair Values of Debt Securities by Contractual Maturity) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Within one year, cost	$ 6.9	$ 2.9
Over one year to five years, cost	55.6	56.9
Over five years to ten years, cost	1.8	2.1
Over ten years, cost	0.1	0.1
Total restricted securities available for sale, cost	64.4	62.0
Within one year, fair value	6.9	3.0
Over one year to five years, fair value	53.8	57.0
Over five years to ten years, fair value	1.6	2.0
Over ten years, fair value	0.1	0.1
Debt Securities, Available-for-sale, Restricted	$ 62.4	$ 62.1

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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