Common Shareholders’ Equity and Non-controlling Interests (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	Sep. 26, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Common Shares Repurchased and Retired
Value of common shares repurchased and retired	$ 460.8	$ 615.8	$ 107.5	$ 85.1
Value of each common share repurchased and retired (in usd per share)	$ 1,400	$ 1,335.11	$ 1,091.29	$ 858.81
Shares repurchased to satisfy employee income tax withholding		4,011	7,218	5,899
Common Shares Issued
Stock issued (in shares)		15,640	15,066	15,745
Dividends on Common Shares
Cash dividends declared and paid		$ 3.0	$ 3.1	$ 3.2
Dividends declared and paid (in usd per share)		$ 1.00
Non-controlling Equity		$ 188.1	$ 156.6
HG Global
Dividends on Common Shares
Non-controlling Percentage		3.10%	3.10%
Ark
Dividends on Common Shares
Non-controlling Percentage		28.00%	28.00%
Kudu
Dividends on Common Shares
Non-controlling Percentage		10.80%	2.50%
NSM
Dividends on Common Shares
Non-controlling Percentage		0.00%	3.50%
BAM
Dividends on Common Shares
Non-controlling Percentage		100.00%	100.00%
Common equity securities
Common Shares Repurchased and Retired
Common shares repurchased and retired (in shares)	327,795	461,256	98,511	99,087
Restricted Stock
Common Shares Issued
Stock issued (in shares)		13,225	13,475	14,055
General Board Authorization
Common Shares Repurchased and Retired
Additional authorized repurchase of common shares (in shares)		320,550
Common shares repurchased and retired (in shares)		129,450	91,293	93,188
Value of common shares repurchased and retired		$ 150.9	$ 100.0	$ 78.5
Value of each common share repurchased and retired (in usd per share)		$ 1,165.84	$ 1,095.37	$ 1,115.51
Directors | Restricted Stock
Common Shares Issued
Shares issued to directors (in shares)		2,415	1,591	1,440
MediaAlpha | Restricted Stock
Common Shares Issued
Stock issued (in shares)				250
HG Global
Dividends on Common Shares
Non-controlling Equity		$ (0.6)	$ 8.9
Ark
Dividends on Common Shares
Non-controlling Equity		247.9	230.7
Kudu
Dividends on Common Shares
Non-controlling Equity		75.1	12.4
NSM
Dividends on Common Shares
Non-controlling Equity		0.0	16.7
Other Operations
Dividends on Common Shares
Non-controlling Equity		20.4	11.9
BAM
Dividends on Common Shares
Non-controlling Equity		(154.7)	(124.0)
Total Non-Controlling Excluding Reciprocals
Dividends on Common Shares
Non-controlling Equity		$ 342.8	$ 280.6