Restricted Securities Available for Sale (Schedule of Restricted Securities Available for Sale by Aging Category) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Restricted Securities Available For Sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 33.3	$ 11.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.2	0.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	34.1	42.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1.5	1.9
Debt Securities, Available-for-sale, Unrealized Loss Position	67.4	53.4
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	1.7	2.0
Corporate Bond Securities [Member]
Restricted Securities Available For Sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	12.0	2.7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.1	0.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	13.8	18.4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.6	0.9
Debt Securities, Available-for-sale, Unrealized Loss Position	25.8	21.1
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.7	0.9
US Government and Agency Securities [Member]
Restricted Securities Available For Sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	13.2	6.8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.1	0.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	13.5	16.4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.7	0.8
Debt Securities, Available-for-sale, Unrealized Loss Position	26.7	23.2
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.8	0.9
Asset-backed Securities [Member]
Restricted Securities Available For Sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	8.1	1.6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	6.7	7.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.2	0.2
Debt Securities, Available-for-sale, Unrealized Loss Position	14.8	8.9
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.2	0.2
Mortgage-backed Securities [Member]
Restricted Securities Available For Sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	0.0	0.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0.1	0.2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	0.0
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 0.1	$ 0.2

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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