Fair Value Measurements - Fair Value Inputs (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions | Sep. 30, 2011 | Dec. 31, 2010 |
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Equity Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | $ 360.8 | $ 550.4 |
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 169.4 | 341.1 |
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 110.0 | 119.4 |
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 81.4 | 89.9 |
Finance Insurance and Real Estate [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 88.9 | 97.7 |
Finance Insurance and Real Estate [Member] | Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Finance Insurance and Real Estate [Member] | Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 88.9 | 97.7 |
Finance Insurance and Real Estate [Member] | Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Preferred Stocks Other Industries [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 20.2 | 27.4 |
Preferred Stocks Other Industries [Member] | Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Preferred Stocks Other Industries [Member] | Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 16.6 | 17.0 |
Preferred Stocks Other Industries [Member] | Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 3.6 | 10.4 |
Intermec [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | | 137.5 |
Intermec [Member] | Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | | 137.5 |
Intermec [Member] | Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | | 0 |
Intermec [Member] | Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | | 0 |
Manufacturing [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 72.3 | 89.6 |
Manufacturing [Member] | Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 65.7 | 82.9 |
Manufacturing [Member] | Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 4.5 | 4.7 |
Manufacturing [Member] | Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 2.1 | 2.0 |
Common Stock Other Industries [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 41.5 | 43.8 |
Common Stock Other Industries [Member] | Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 38.0 | 41.5 |
Common Stock Other Industries [Member] | Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Common Stock Other Industries [Member] | Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 3.5 | 2.3 |
Exchange Traded Funds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 65.7 | 79.2 |
Exchange Traded Funds [Member] | Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 65.7 | 79.2 |
Exchange Traded Funds [Member] | Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Exchange Traded Funds [Member] | Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Partnership Interest [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 72.2 | 75.2 |
Partnership Interest [Member] | Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Partnership Interest [Member] | Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Partnership Interest [Member] | Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 72.2 | 75.2 |
Debt Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 4,782.4 | 4,475.3 |
Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 153.4 | 281.0 |
Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 4,437.6 | 4,043.2 |
Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 191.4 | 151.1 |
US Government and Government Agencies and Authorities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 516.7 | 536.9 |
US Government and Government Agencies and Authorities [Member] | Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 153.4 | 281.0 |
US Government and Government Agencies and Authorities [Member] | Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 363.3 | 255.9 |
US Government and Government Agencies and Authorities [Member] | Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
US States and Political Subdivisions Debt Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 1,903.3 | 1,792.8 |
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 1,903.3 | 1,792.8 |
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Corporate Debt Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 2,275.2 | 2,049.0 |
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 2,088.6 | 1,902.8 |
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 186.6 | 146.2 |
Redeemable Preferred Stock [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 81.5 | 88.3 |
Redeemable Preferred Stock [Member] | Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Redeemable Preferred Stock [Member] | Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 77.0 | 83.8 |
Redeemable Preferred Stock [Member] | Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 4.5 | 4.5 |
Asset-backed Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 5.7 | 8.3 |
Asset-backed Securities [Member] | Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0 | 0 |
Asset-backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 5.4 | 7.9 |
Asset-backed Securities [Member] | Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Available-for-sale Securities, Fair Value Disclosure | 0.3 | 0.4 |
Estimate of Fair Value, Fair Value Disclosure [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Trading Securities, Fair Value Disclosure | | 5.1 |
| Investments, Fair Value Disclosure | 5,147.4 | 5,030.8 |
Fair Value, Inputs, Level 1 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Trading Securities, Fair Value Disclosure | 4.2 | 5.1 |
| Investments, Fair Value Disclosure | 327.0 | 627.2 |
Fair Value, Inputs, Level 2 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Trading Securities, Fair Value Disclosure | 0 | 0 |
| Investments, Fair Value Disclosure | 4,547.6 | 4,162.6 |
Fair Value, Inputs, Level 3 [Member] | | |
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
| Trading Securities, Fair Value Disclosure | 0 | 0 |
| Investments, Fair Value Disclosure | $ 272.8 | $ 241.0 |