Discontinued Operations (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Discontinued Operation, Income (Loss) from Discontinued Operation Disclosures [Abstract]
Income Tax Expense									$ (0.5)	$ (2.2)	$ (3.1)
Income from Discontinued Operations	$ 1.0	$ (0.1)	$ 0.0	$ 0.1	$ 2.1	$ 2.0	$ (0.1)	$ 0.1	$ 1.0	$ 4.1	$ 5.5
Income from Discontinued Operations Per Unrestricted Share:
Basic (in dollars per share)									$ 0.02	$ 0.08	$ 0.10
Diluted (in dollars per share)									$ 0.02	$ 0.08	$ 0.10
Property and Casualty	1,016.8				931.4				$ 1,016.8	$ 931.4	$ 862.8	$ 733.9
Unitrin Business Insurance [Member]
Discontinued Operation, Income (Loss) from Discontinued Operation Disclosures [Abstract]
Results of Operations									1.5	6.3	$ 8.6
Income from Discontinued Operations Per Unrestricted Share:
Property and Casualty	$ 32.8				$ 38.3				$ 32.8	$ 38.3