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Common Shareholders’ Equity and Non-controlling Interests (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Common Shares Repurchased and Retired [Abstract] |  |  |
Value of common shares repurchased and retired during the period | $ 4.9 | $ 519.1 | $ 723.9
Value of each common share repurchased and retired during the period (in dollars per share) | $ 858 | $ 877 | $ 869
Common Shares Issued [Abstract] |  |  |
Stock issued during period, shares, new issues | 17,917 | 16,377 | 25,086
Shares issued to directors (in shares) | 2,317 | 2,272 |
Dividends, Common Stock [Abstract] |  |  |
Cash dividends declared and paid | $ 3.2 | $ 3.8 | $ 4.6
Dividends delared and paid (in dollars per share) | $ 1.00 |  |
Noncontrolling interest, ownership percentage by noncontrolling owners |  |  |
Non-controlling interests | $ (116.8) | $ (124.9) |
Common Stock |  |  |
Common Shares Repurchased and Retired [Abstract] |  |  |
Common shares repurchased and retired during the period | 5,679 | 592,458 | 832,725
Restricted Stock |  |  |
Common Shares Issued [Abstract] |  |  |
Stock issued during period, shares, new issues | 15,600 | 14,105 | 17,985
General Board Authorization |  |  |
Common Shares Repurchased and Retired [Abstract] |  |  |
Additional authorized repurchase of common shares | 635,705 |  |
Common shares repurchased and retired during the period |  | 582,493 | 821,732
Value of common shares repurchased and retired during the period |  | $ 511.0 | $ 713.1
Value of each common share repurchased and retired during the period (in dollars per share) |  | $ 877 | $ 870
Chief Executive Officer | Restricted Stock |  |  |
Common Shares Issued [Abstract] |  |  |
Stock issued during period, shares, new issues |  |  | 5,142
Directors | Restricted Stock |  |  |
Common Shares Issued [Abstract] |  |  |
Stock issued during period, shares, new issues |  |  | 1,959
Repurchased for Employee Benefit Plans |  |  |
Common Shares Repurchased and Retired [Abstract] |  |  |
Common shares repurchased and retired during the period |  | 9,965 | 10,993
HG Global |  |  |
Dividends, Common Stock [Abstract] |  |  |
Noncontrolling interest, ownership percentage by noncontrolling owners | 3.10% | 3.10% |
Non-controlling interests | $ 14.4 | $ 14.5 |
NSM Insurance HoldCo, LLC |  |  |
Dividends, Common Stock [Abstract] |  |  |
Noncontrolling interest, ownership percentage by noncontrolling owners | 3.60% | 4.50% |
Non-controlling interests | $ 14.9 | $ 13.6 |
Other NSM |  |  |
Dividends, Common Stock [Abstract] |  |  |
Noncontrolling interest, ownership percentage by noncontrolling owners | 13.40% | 13.40% |
Non-controlling interests | $ (0.1) | $ 0.3 |
Kudu |  |  |
Dividends, Common Stock [Abstract] |  |  |
Noncontrolling interest, ownership percentage by noncontrolling owners | 0.00% | 0.00% |
Non-controlling interests | $ 2.2 | $ 0.0 |
MediaAlpha |  |  |
Dividends, Common Stock [Abstract] |  |  |
Noncontrolling interest, ownership percentage by noncontrolling owners | 0.00% | 39.00% |
Non-controlling interests | $ 0.0 | $ 16.2 |
Other |  |  |
Dividends, Common Stock [Abstract] |  |  |
Non-controlling interests | $ (1.5) | $ 1.1 |
BAM |  |  |
Dividends, Common Stock [Abstract] |  |  |
Noncontrolling interest, ownership percentage by noncontrolling owners | 100.00% | 100.00% |
Non-controlling interests | $ (146.7) | $ (170.6) |
Total Non-Controlling Excluding Reciprocals |  |  |
Dividends, Common Stock [Abstract] |  |  |
Non-controlling interests | $ 29.9 | $ 45.7 |

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