| **Segment Information (Tables)** | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
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| **Segment Reporting [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| Segment Information              | This table summarizes segment information:(In millions) Years ended December 31,  2013 2012 2011Revenues:      Commercial lines insurance      Commercial casualty $856 $767 $711Commercial property 623 545 497Commercial auto 479 426 394Workers' compensation 365 344 318Specialty packages 150 151 138Management liability and surety 119 111 103Machinery and equipment 44 39 36Commercial lines insurance premiums 2,636 2,383 2,197Fee revenue 3 4 3Total commercial lines insurance 2,639 2,387 2,200       Personal lines insurance      Personal auto 443 404 368Homeowner 403 353 294Other personal lines 115 111 100Personal lines insurance premiums 961 868 762Fee revenue 1 2 1Total personal lines insurance 962 870 763       Excess and surplus lines insurance 116 93 70       Life insurance premiums 189 178 165Separate account investment management fees 4 1 2Total life insurance 193 179 167       Investment operations      Investment income, net of expenses 529 531 525Realized investment gains, net 83 42 70Total investment revenue 612 573 595       Other 9 9 8Total revenues $4,531 $4,111 $3,803       Income (loss) before income taxes:      Insurance underwriting results:      Commercial lines insurance $186 $181 $(102)Personal lines insurance 33 (43) (182)Excess and surplus lines insurance 14 (1) 6Life insurance 9 (3) (3)Investment operations 532 491 514Other (60) (59) (60)Total income before income taxes $714 $566 $173       Identifiable assets: December 31, December 31,    2013 2012  Property casualty insurance $2,455 $2,395  Life insurance 1,225 1,201  Investment operations 13,618 12,599  Other 364 353  Total $17,662 $16,548          |

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| - Definition
Tabular disclosure of the profit or loss and total assets for each reportable segment. An entity discloses certain information on each reportable segment if the amounts (a) are included in the measure of segment profit or loss reviewed by the chief operating decision maker or (b) are otherwise regularly provided to the chief operating decision maker, even if not included in that measure of segment profit or loss.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8721-108599Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 25 -URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8813-108599Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=14024403&loc=d3e13816-109267Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 30 -URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8906-108599Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 22 -URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8736-108599
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