Commitments and Contingent Liabilities (Tables)

12 Months Ended

Dec. 31, 2020

Commitments and Contingencies Disclosure [Abstract]

Reinsurance Ceded and Other Related Data

Years Ended December 31:		2020		2019		2018
General Insurance Group
Written premiums:	Direct	$	5,206.9	$	4,966.4	$	4,673.4
	Assumed	70.6		66.9		58.1
	Ceded	$	1,846.2	$	1,564.3	$	1,351.1
Earned premiums:	Direct	$	5,030.2	$	4,857.0	$	4,534.8
	Assumed	70.3		56.4		55.8
	Ceded	$	1,706.3	$	1,481.1	$	1,313.5
Claims ceded		$	1,100.7	$	910.2	$	745.0
RFIG Run-off Business
Written premiums:	Direct	$	44.3	$	57.5	$	73.9
	Assumed	—		—		—
	Ceded	$	—	$	—	$	—
Earned premiums:	Direct	$	45.1	$	59.2	$	75.9
	Assumed	—		—		—
	Ceded	$	—	$	—	$	—
Claims ceded		$	—	$	—	$	—
Mortgage Guaranty Insurance in force as of December 31:
	Direct	$	7,883.2	$	10,156.8	$	13,100.5
	Assumed	—		—		—
	Ceded	$	—	$	—	$	—

Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]

The following table presents a summary of future undiscounted lease payments as of the dates shown.

																	Lease
	Year 1		Year 2		Year 3		Year 4		Year 5		Thereafter		Total		Discount		Liability
December 31, 2020	$	61.3	$	54.0	$	43.7	$	34.0	$	27.1	$	96.4	$	316.8	$	69.3	$	247.6
December 31, 2019	$	59.0	$	50.6	$	42.9	$	33.5	$	24.4	$	100.9	$	311.6	$	73.6	$	238.0