Schedule III and VI Supplementary Insurance Information Supplemental Information Concerning Property and Casualty Insurance Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	$ 433.1	$ 248.0	$ 229.8
Future policy benefits, claims and claim expenses	7,553.1	7,003.7	6,884.1
Unearned premiums	264.2	255.1	264.5
Other policy claims and benefits payable	954.0	945.9	751.3
Premium revenue/ premium earned	1,029.0	889.6	930.7
Net investment income	400.9	422.5	357.6
Benefits, claims and settlement expenses	939.2	782.1	773.5
Amortization of deferred policy acquisition costs	98.7	94.7	99.9
Other operating expenses	356.9	278.4	277.4
Property & Casualty
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	24.5	24.4	26.1
Future policy benefits, claims and claim expenses	388.7	362.4	372.1
Unearned premiums	259.1	249.8	259.4
Other policy claims and benefits payable	0.0	0.0	0.0
Premium revenue/ premium earned	608.2	617.4	650.1
Net investment income	31.4	61.1	42.6
Benefits, claims and settlement expenses	534.3	447.9	431.0
Amortization of deferred policy acquisition costs	64.3	67.7	74.4
Other operating expenses	102.6	97.2	97.7
Net premiums written (excluding life)	617.5	607.8	635.5
Life & Retirement
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	403.5	219.4	199.4
Future policy benefits, claims and claim expenses	6,323.9	6,247.4	6,119.6
Unearned premiums	2.1	2.2	2.0
Other policy claims and benefits payable	860.6	873.4	709.8
Premium revenue/ premium earned	145.3	144.2	147.0
Net investment income	338.3	338.6	299.3
Benefits, claims and settlement expenses	303.8	292.9	298.2
Amortization of deferred policy acquisition costs	32.8	25.5	23.8
Other operating expenses	108.6	102.4	105.4
Supplemental & Group Benefits
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Deferred policy acquisition costs	5.1	4.2	4.3
Future policy benefits, claims and claim expenses	840.5	393.9	392.4
Unearned premiums	3.0	3.1	3.1
Other policy claims and benefits payable	93.4	72.5	41.5
Premium revenue/ premium earned	275.5	128.0	133.6
Net investment income	33.3	25.2	18.1
Benefits, claims and settlement expenses	101.1	41.3	44.3
Amortization of deferred policy acquisition costs	1.6	1.5	1.7
Other operating expenses	118.1	54.4	53.6
Other, including consolidating eliminations | Eliminations
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Line Items]
Net investment income	(2.1)	(2.4)	(2.4)
Other operating expenses	$ 27.6	$ 24.4	$ 20.7