Income Tax Matters - Income Tax Benefit (Provision) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Federal income tax (expense) benefit
Current federal tax (expense) benefit		$ 6.1	$ 5.7
Deferred federal income tax (expense) benefit	$ 2.1	(18.8)	(19.6)
Federal benefit (expense) applied to decrease (increase) Other comprehensive income	3.7	5.1	2.7
Federal income tax benefit (provision)	5.8	(7.6)	(11.2)
Foreign income tax (expense) benefit
Current foreign tax (expense) benefit	(2.4)	(0.4)	(1.1)
Deferred foreign income tax (expense) benefit	0.5	(0.1)	(0.3)
Foreign benefit (expense) applied to decrease (increase) Other comprehensive income	0.3	(0.1)	(0.1)
Foreign income tax benefit (provision)	(1.6)	(0.6)	(1.5)
State income tax (expense) benefit
Current state tax (expense) benefit	(3.5)	(0.6)	(1.8)
Deferred state income tax (expense) benefit	4.2	(2.3)	(4.5)
State benefit (expense) applied to decrease (increase) Other comprehensive income	0.6	1.1	0.6
State income tax benefit (provision)	1.3	(1.8)	(5.7)
Total income tax (expense) benefit
Current tax (expense) benefit	(5.9)	5.1	2.8
Deferred income tax (expense) benefit	6.8	(21.2)	(24.4)
Benefit (expense) applied to decrease (increase) Other comprehensive income	4.6	6.1	3.2
Income tax benefit (provision)	$ 5.5	$ (10.0)	$ (18.4)