3. Fair Value and Gross Unrealized Losses with Unrealized Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Price Change Debt Security	5.00%
Tolerable variance Level 2 debt security pricing	1.00%
Fair Value of Investments with Gross Unrealized Losses in loss position 12 months or more	$ 3.7	$ 19.9
Fair Value of Investments with Gross Unrealized Losses in loss position less than 12 months	161.2	91.9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.1	0.1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	164.9	111.8
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	2.4	0.4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2.3	0.3
Corporate Debt Securities [Member]
Fair Value of Investments with Gross Unrealized Losses in loss position 12 months or more	0.0	2.1
Fair Value of Investments with Gross Unrealized Losses in loss position less than 12 months	106.0	46.5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	106.0	48.6
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1.7	0.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1.7	0.1
US Government Sponsored Agencies [Member]
Fair Value of Investments with Gross Unrealized Losses in loss position 12 months or more		10.8
Fair Value of Investments with Gross Unrealized Losses in loss position less than 12 months		27.5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax		38.3
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		0.2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		0.2
Asset-backed Securities [Member]
Fair Value of Investments with Gross Unrealized Losses in loss position 12 months or more	3.7	7.0
Fair Value of Investments with Gross Unrealized Losses in loss position less than 12 months	55.2	17.9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.1	0.1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	58.9	24.9
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0.7	0.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.6	$ 0.0
Fair Value, Recurring [Member] | Debt Securities [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 2.4