Restricted Securities Available for Sale (Schedule of Restricted Securities Available for Sale) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	$ 79.1	$ 76.1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.2	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2.9	3.8
Debt Securities, Available-for-sale, Restricted	76.4	72.3
Corporate Bond Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	35.1	32.6
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.1	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1.5	1.7
Debt Securities, Available-for-sale, Restricted	33.7	30.9
US Government and Agency Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	28.8	29.5
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.1	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	1.1	1.7
Debt Securities, Available-for-sale, Restricted	27.8	27.8
Asset-backed Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	15.0	13.8
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.3	0.4
Debt Securities, Available-for-sale, Restricted	14.7	13.4
Mortgage-backed Securities [Member]
Restricted Securities Available For Sale [Line Items]
Total restricted securities available for sale, cost	0.2	0.2
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Restricted	$ 0.2	$ 0.2

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
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-Publisher FASB
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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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