| **Business Segments (Tables)**                                                                 | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       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| **Business Segments [Abstract]**                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                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| Significant components of the Company's continuing operations and selected balance sheet items | Year ended December 31, 2011CNASpecialty CNACommercial Life &GroupNon-Core Corporate& OtherNon-Core    (In millions)    Eliminations TotalNet written premiums (a)$2,872 $3,350 $577 $2 $(3) $6,798Operating revenues           Net earned premiums$2,796 $3,240 $569 $1 $(3) $6,603Net investment income500 763 759 32 — 2,054Other revenues221 54 13 6 — 294Total operating revenues3,517 4,057 1,341 39 (3) 8,951Claims, Benefits and Expenses           Net incurred claims and benefits1,657 2,296 1,526 (3) — 5,476Policyholders’ dividends(3) 8 8 — — 13Amortization of deferred acquisition costs663 725 22 — — 1,410Other insurance related expenses197 395 143 6 (3) 738Other expenses191 53 19 170 — 433Total claims, benefits and expenses2,705 3,477 1,718 173 (3) 8,070Operating income (loss) from continuing operations before income tax812 580 (377) (134) — 881Income tax (expense) benefit on operating income (loss)(281) (207) 169 68 — (251)Net operating (income) loss, after-tax, attributable to noncontrolling interests(12) (4) — — — (16)Net operating income (loss) from continuing operations attributable to CNA519 369 (208) (66) — 614Net realized investment gains (losses), net of participating policyholders’ interests(5) 14 (7) (6) — (4)Income tax (expense) benefit on net realized investment gains (losses)2 (2) 2 3 — 5Net realized investment (gains) losses, after-tax, attributable to noncontrolling interests— — — — — —Net realized investment gains (losses) attributable to CNA(3) 12 (5) (3) — 1Net income (loss) from continuing operations attributable to CNA$516 $381 $(213) $(69) $— $615(a) Related to business in property and casualty companies only.December 31, 2011           (In millions)           Reinsurance receivables$852 $1,188 $1,375 $2,677 $— $6,092Insurance receivables$670 $1,047 $8 $1 $— $1,726Deferred acquisition costs$347 $311 $— $— $— $658Insurance reserves           Claim and claim adjustment expenses$6,840 $11,509 $2,825 $3,129 $— $24,303Unearned premiums1,629 1,480 141 — — 3,250Future policy benefits— — 9,810 — — 9,810Policyholders’ funds15 10 166 — — 191Year ended December 31, 2010CNASpecialty CNACommercial Life &GroupNon-Core Corporate& OtherNon-Core    (In millions)    Eliminations TotalNet written premiums (a)$2,691 $3,208 $573 $2 $(3) $6,471Operating revenues           Net earned premiums$2,679 $3,256 $582 $1 $(3) $6,515Net investment income591 873 715 137 — 2,316Other revenues216 61 7 8 — 292Total operating revenues3,486 4,190 1,304 146 (3) 9,123Claims, Benefits and Expenses           Net incurred claims and benefits1,447 2,175 1,275 58 — 4,955Policyholders’ dividends12 14 4 — — 30Amortization of deferred acquisition costs631 736 20 — — 1,387Other insurance related expenses186 424 180 10 (3) 797Other expenses190 55 2 681 — 928Total claims, benefits and expenses2,466 3,404 1,481 749 (3) 8,097Operating income (loss) from continuing operations before income tax1,020 786 (177) (603) — 1,026Income tax (expense) benefit on operating income (loss)(343) (260) 90 216 — (297)Net operating (income) loss, after-tax, attributable to noncontrolling interests(52) (17) — — — (69)Net operating income (loss) from continuing operations attributable to CNA625 509 (87) (387) — 660Net realized investment gains (losses), net of participating policyholders’ interests30 (15) 53 18 — 86Income tax (expense) benefit on net realized investment gains (losses)(10) (1) (20) (5) — (36)Net realized investment (gains) losses, after-tax, attributable to noncontrolling interests— 1 — — — 1Net realized investment gains (losses) attributable to CNA20 (15) 33 13 — 51Net income (loss) from continuing operations attributable to CNA$645 $494 $(54) $(374) $— $711(a) Related to business in property and casualty companies only.December 31, 2010           (In millions)           Reinsurance receivables$906 $1,973 $1,502 $2,823 $— $7,204Insurance receivables$654 $1,050 $9 $4 $— $1,717Deferred acquisition costs$330 $315 $434 $— $— $1,079Insurance reserves      Claim and claim adjustment expenses$6,793 $12,522 $2,739 $3,442 $— $25,496Unearned premiums1,543 1,526 132 2 — 3,203Future policy benefits— — 8,718 — — 8,718Policyholders’ funds16 13 144 — — 173Year ended December 31, 2009CNASpecialty CNACommercial Life &GroupNon-Core Corporate& OtherNon-Core    (In millions)    Eliminations TotalNet written premiums (a)$2,684 $3,448 $583 $1 $(3) $6,713Operating revenues           Net earned premiums$2,697 $3,432 $595 $— $(3) $6,721Net investment income526 935 664 195 — 2,320Other revenues206 61 11 10 — 288Total operating revenues3,429 4,428 1,270 205 (3) 9,329Claims, Benefits and Expenses           Net incurred claims and benefits1,536 2,420 1,084 227 — 5,267Policyholders’ dividends9 9 5 — — 23Amortization of deferred acquisition costs624 775 18 — — 1,417Other insurance related expenses163 435 183 3 (3) 781Other expenses179 77 69 119 — 444Total claims, benefits and expenses2,511 3,716 1,359 349 (3) 7,932Operating income (loss) from continuing operations before income tax918 712 (89) (144) — 1,397Income tax (expense) benefit on operating income (loss)(282) (201) 73 57 — (353)Net operating (income) loss, after-tax, attributable to noncontrolling interests(45) (17) — — — (62)Net operating income (loss) from continuing operations attributable to CNA591 494 (16) (87) — 982Net realized investment gains (losses), net of participating policyholders’ interests(186) (360) (235) (76) — (857)Income tax (expense) benefit on net realized investment gains (losses)64 123 82 27 — 296Net realized investment (gains) losses, after-tax, attributable to noncontrolling interests(1) 1 — — — —Net realized investment gains (losses) attributable to CNA(123) (236) (153) (49) — (561)Net income (loss) from continuing operations attributable to CNA$468 $258 $(169) $(136) $— $421(a) Related to business in property and casualty companies only. |
| Revenues by line of business                                                                   | Revenues by Line of BusinessYears ended December 31     (In millions)2011 2010 2009CNA Specialty     International$210 $199 $171Professional & Management Liability2,541 2,551 2,339Surety472 475 474Warranty & Alternative Risks289 291 259CNA Specialty revenues3,512 3,516 3,243CNA Commercial     CNA Select Risk272 261 210Commercial Insurance2,681 2,851 2,692International537 499 617Small Business581 564 549CNA Commercial revenues4,071 4,175 4,068Life & Group Non-Core     Health1,093 1,100 811Life & Annuity229 249 211Other12 8 13Life & Group Non-Core revenues1,334 1,357 1,035Corporate & Other Non-Core revenues33 164 129Eliminations(3) (3) (3)Total revenues$8,947 $9,209 $8,472                                                                                                                                                                                                                               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| - Definition
Tabular disclosure of all significant reconciling items in the reconciliation of total revenues from reportable segments to the entity's consolidated revenues.
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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.
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