Restricted Securities Available for Sale (Schedule of Restricted Securities Available for Sale by Aging Category) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Restricted Securities Available For Sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 42.5	$ 40.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.9	1.5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	42.2	26.9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2.9	2.3
Debt Securities, Available-for-sale, Unrealized Loss Position	84.7	66.9
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	3.8	3.8
Corporate Bond Securities [Member]
Restricted Securities Available For Sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	18.5	15.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.4	0.6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	16.8	13.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1.2	1.1
Debt Securities, Available-for-sale, Unrealized Loss Position	35.3	28.4
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	1.6	1.7
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	13.9	18.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.4	0.8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	18.8	9.2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1.3	0.9
Debt Securities, Available-for-sale, Unrealized Loss Position	32.7	27.2
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	1.7	1.7
Asset-backed Securities [Member]
Restricted Securities Available For Sale [Line Items]
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	10.1	6.6
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	6.4	4.4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.4	0.3
Debt Securities, Available-for-sale, Unrealized Loss Position	16.5	11.0
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.5	0.4
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	0.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0.2	0.0
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	$ 0.2	$ 0.3