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Common Shareholders’ Equity and Non-controlling Interests (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Common Shares Repurchased and Retired
Value of common shares repurchased and retired	$ 85.1	$ 4.9	$ 519.1
Value of each common share repurchased and retired (in usd per share)	$ 859	$ 858	$ 877
Common Shares Issued
Stock issued (in shares)	15,745	17,917	16,377
Dividends on Common Shares
Cash dividends declared and paid	$ 3.2	$ 3.2	$ 3.8
Dividends declared and paid (in usd per share)	$ 1.00
Non-controlling interests	$ (88.1)	$ (116.8)
HG Global
Dividends on Common Shares
Non-controlling Percentage	3.10%	3.10%
NSM
Dividends on Common Shares
Non-controlling Percentage	3.40%	3.60%
Kudu
Dividends on Common Shares
Non-controlling Percentage	0.70%	0.90%
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)	99,087	5,679	592,458
Restricted Stock
Common Shares Issued
Stock issued (in shares)	14,055	15,600	14,105
General Board Authorization
Common Shares Repurchased and Retired
Additional authorized repurchase of common shares (in shares)	542,517
Common shares repurchased and retired (in shares)	93,188		582,493
Value of common shares repurchased and retired	$ 78.5		$ 511.0
Value of each common share repurchased and retired (in usd per share)	$ 843		$ 877
Directors | Restricted Stock
Common Shares Issued
Shares issued to directors (in shares)	1,440	2,317	2,272
Repurchased for Employee Benefit Plans
Common Shares Repurchased and Retired
Common shares repurchased and retired (in shares)	5,899		9,965
MediaAlpha | Restricted Stock
Common Shares Issued
Stock issued (in shares)	250
HG Global
Dividends on Common Shares
Non-controlling interests	$ 13.5	$ 14.4
NSM
Dividends on Common Shares
Non-controlling interests	17.0	14.9
Kudu
Dividends on Common Shares
Non-controlling interests	2.3	2.2
Other
Dividends on Common Shares
Non-controlling interests	2.4	(1.6)
BAM
Dividends on Common Shares
Non-controlling interests	(123.3)	(146.7)
Total Non-Controlling Excluding Reciprocals
Dividends on Common Shares
Non-controlling interests	$ 35.2	$ 29.9

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