Restricted Securities Available for Sale (Schedule of Restricted Securities Available for Sale by Aging Category) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Restricted Securities Available For Sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 3.4	$ 11.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.0	0.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	23.7	42.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.6	1.9
Debt Securities, Available-for-sale, Unrealized Loss Position	27.1	53.4
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.6	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	2.9	2.7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.0	0.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	9.6	18.4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.3	0.9
Debt Securities, Available-for-sale, Unrealized Loss Position	12.5	21.1
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.3	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	0.5	6.8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.0	0.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	10.4	16.4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.3	0.8
Debt Securities, Available-for-sale, Unrealized Loss Position	10.9	23.2
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.3	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	0.0	1.6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	3.6	7.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	0.2
Debt Securities, Available-for-sale, Unrealized Loss Position	3.6	8.9
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss		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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