Restricted Securities Available for Sale (Schedule of Restricted Securities Available for Sale by Aging Category) (Details) - USD ($) $ in Millions	Jun. 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	$ 55.5	$ 40.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1.6	1.5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	22.3	26.9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1.9	2.3
Debt Securities, Available-for-sale, Unrealized Loss Position	77.8	66.9
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	3.5	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	21.3	15.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.6	0.6
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	11.4	13.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1.0	1.1
Debt Securities, Available-for-sale, Unrealized Loss Position	32.7	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	21.5	18.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.8	0.8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	7.6	9.2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.7	0.9
Debt Securities, Available-for-sale, Unrealized Loss Position	29.1	27.2
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	1.5	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	12.5	6.6
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	3.3	4.4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.2	0.3
Debt Securities, Available-for-sale, Unrealized Loss Position	15.8	11.0
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.4	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	0.2	0.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0.0	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