| **Business Segments (Tables)**                                                                 | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   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| **Segment Reporting [Abstract]**                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           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| Significant components of the Company's continuing operations and selected balance sheet items | The Company's results of operations and selected balance sheet items by segment are presented in the following tables.Three months ended March 31, 2016 Specialty Commercial International Life &GroupNon-Core Corporate& OtherNon-Core    (In millions)     Eliminations TotalOperating revenues             Net earned premiums$682 $688 $198 $131 $— $— $1,699Net investment income107 126 12 187 3 — 435Other revenues87 6 1 — 3 — 97Total operating revenues876 820 211 318 6 — 2,231Claims, Benefits and Expenses             Net incurred claims and benefits390 442 121 323 128 — 1,404Policyholders’ dividends1 3 — — — — 4Amortization of deferred acquisition costs144 116 47 — — — 307Other insurance related expenses75 141 28 33 — — 277Other expenses75 5 9 3 54 — 146Total claims, benefits and expenses685 707 205 359 182 — 2,138Operating income (loss) before income tax191 113 6 (41) (176) — 93Income tax (expense) benefit on operating income (loss)(64) (39) — 39 62 — (2)Net operating income (loss) 127 74 6 (2) (114) — 91Net realized investment gains (losses)(11) (18) 4 (3) (8) — (36)Income tax (expense) benefit on net realized investment gains (losses)4 6 (1) — 2 — 11Net realized investment gains (losses), after tax(7) (12) 3 (3) (6) — (25)Net income (loss)$120 $62 $9 $(5) $(120) $— $66March 31, 2016             (In millions)             Reinsurance receivables$765 $623 $139 $496 $2,707 $— $4,730Insurance receivables884 1,025 276 14 2 — 2,201Deferred acquisition costs309 225 88 — — — 622Goodwill117 — 33 — — — 150Insurance reserves             Claim and claim adjustment expenses6,325 9,095 1,395 3,311 2,892 — 23,018Unearned premiums1,861 1,347 464 136 — (1) 3,807Future policy benefits— — — 10,500 — — 10,500Three months ended March 31, 2015Specialty Commercial International Life &GroupNon-Core Corporate& OtherNon-Core    (In millions)    Eliminations TotalOperating revenues             Net earned premiums$680 $678 $191 $138 $— $— $1,687Net investment income155 204 14 179 6 — 558Other revenues78 9 — 9 2 (1) 97Total operating revenues913 891 205 326 8 (1) 2,342Claims, Benefits and Expenses             Net incurred claims and benefits429 454 116 340 (4) — 1,335Policyholders’ dividends1 3 — — — — 4Amortization of deferred acquisition costs144 117 35 7 — — 303Other insurance related expenses69 127 37 35 — — 268Other expenses67 8 5 4 46 (1) 129Total claims, benefits and expenses710 709 193 386 42 (1) 2,039Operating income (loss) before income tax203 182 12 (60) (34) — 303Income tax (expense) benefit on operating income (loss)(68) (62) (3) 43 12 — (78)Net operating income (loss)135 120 9 (17) (22) — 225Net realized investment gains (losses)4 4 1 1 — — 10Income tax (expense) benefit on net realized investment gains (losses)(1) (3) — 2 — — (2)Net realized investment gains (losses), after tax3 1 1 3 — — 8Net income (loss)$138 $121 $10 $(14) $(22) $— $233December 31, 2015             (In millions)             Reinsurance receivables$724 $639 $144 $497 $2,487 $— $4,491Insurance receivables890 993 233 11 2 — 2,129Deferred acquisition costs307 213 78 — — — 598Goodwill117 — 33 — — — 150Insurance reserves             Claim and claim adjustment expenses6,269 9,183 1,347 3,220 2,644 — 22,663Unearned premiums1,839 1,297 415 120 — — 3,671Future policy benefits— — — 10,152 — — 10,152 |
| Revenues by line of business                                                                   | The following table presents revenue by line of business for each reportable segment. Revenues are comprised of Operating revenues and Net realized investment gains and losses.Three months ended March 31   (In millions)2016 2015Specialty   Management & Professional Liability$618 $697Surety127 120Warranty & Alternative Risks120 100Specialty revenues865 917Commercial   Middle Market401 409Small Business143 165Other Commercial Insurance258 321Commercial revenues802 895International Canada50 55CNA Europe78 77Hardy87 74International revenues215 206Life & Group Non-Core revenues315 327Corporate & Other Non-Core revenues(2) 8Eliminations— (1)Total revenues$2,195 $2,352                                                                                                                                                                                                                                                                                                                                                                                                                                 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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.
+ References
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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
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| - References
No definition available.
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