Income from Continuing Operations Per Unrestricted Share - Reconciliation of Numerator and Denominator in Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted-average Unrestricted Shares Outstanding (in shares)		64,025,600	63,825,500	64,264,400
Equity-based Compensation Equivalent Shares (in shares)		0	0	0
Weighted-average Unrestricted Shares and Equivalent Shares Outstanding Assuming Dilution (in shares)		64,025,600	63,825,500	64,264,400
Basic Income from Continuing Operations Per Unrestricted Share (in dollars per share)	$ (1.92)			$ (1.92)
Diluted Income from Continuing Operations Per Unrestricted Share (in dollars per share)	$ (1.92)			$ (1.92)
Net Loss attributable to Kemper Corporation		$ (272.1)	$ (286.6)	$ (123.7)