Common Shareholders’ Equity and Non-controlling Interests (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Common Shares Repurchased and Retired
Value of common shares repurchased and retired	$ 107.5	$ 85.1	$ 4.9
Value of each common share repurchased and retired (in usd per share)	$ 1,091	$ 859	$ 858
Common Shares Issued
Stock issued (in shares)	15,066	15,745	17,917
Dividends on Common Shares
Cash dividends declared and paid	$ 3.1	$ 3.2	$ 3.2
Dividends declared and paid (in usd per share)	$ 1.00
Non-controlling Equity	$ 156.6	$ (88.1)
HG Global
Dividends on Common Shares
Non-controlling Percentage	3.10%	3.10%
Ark
Dividends on Common Shares
Non-controlling Percentage	28.00%	0.00%
NSM
Dividends on Common Shares
Non-controlling Percentage	3.50%	3.40%
Kudu
Dividends on Common Shares
Non-controlling Percentage	2.50%	0.70%
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)	98,511	99,087	5,679
Restricted Stock
Common Shares Issued
Stock issued (in shares)	13,475	14,055	15,600
General Board Authorization
Common Shares Repurchased and Retired
Additional authorized repurchase of common shares (in shares)	451,224
Common shares repurchased and retired (in shares)	91,293
Value of common shares repurchased and retired	$ 100.0
Value of each common share repurchased and retired (in usd per share)	$ 1,095
Directors | Restricted Stock
Common Shares Issued
Shares issued to directors (in shares)	1,591	1,440	2,317
Repurchased for Employee Benefit Plans
Common Shares Repurchased and Retired
Common shares repurchased and retired (in shares)	7,218
MediaAlpha | Restricted Stock
Common Shares Issued
Stock issued (in shares)		250
HG Global
Dividends on Common Shares
Non-controlling Equity	$ 8.9	$ 13.5
Ark
Dividends on Common Shares
Non-controlling Equity	230.7	0.0
NSM
Dividends on Common Shares
Non-controlling Equity	16.7	17.0
Kudu
Dividends on Common Shares
Non-controlling Equity	12.4	2.3
Other
Dividends on Common Shares
Non-controlling Equity	11.9	2.4
BAM
Dividends on Common Shares
Non-controlling Equity	(124.0)	(123.3)
Total Non-Controlling Excluding Reciprocals
Dividends on Common Shares
Non-controlling Equity	$ 280.6	$ 35.2