Segments Information - Revenues and Income Before Income Tax of Each Operating Segment (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues
Premiums earned related to insurance business	$ 3,134	$ 3,063	$ 6,239	$ 6,092
Premiums earned related to reinsurance assumed	(1)	1	(1)	1
Net Premiums earned	3,133	3,064	6,238	6,093
Investment Income	334	351	673	709
Corporate and other	8	8	17	18
Realized investment gains, net	20	125	31	241
Total Revenues	3,489	3,542	6,946	7,048
Insurance underwriting income (loss)	397	256	585	451
Reinsurance assumed underwriting income	3	1	3	1
Underwriting income before deferred policy acquisition costs	400	257	588	452
Increase in deferred policy acquisition costs	28	21	45	34
Underwriting income	428	278	633	486
Total property and casualty insurance	739	612	1,272	1,159
Corporate and other	(81)	(59)	(143)	(119)
Realized investment gains, net	20	125	31	241
Income Before Federal and Foreign Income Tax	678	678	1,160	1,281
Personal Insurance [Member]
Revenues
Premiums earned related to insurance business	1,137	1,102	2,250	2,178
Insurance underwriting income (loss)	89	45	59	47
Commercial Insurance [Member]
Revenues
Premiums earned related to insurance business	1,345	1,305	2,687	2,605
Insurance underwriting income (loss)	148	71	239	182
Specialty Insurance [Member]
Revenues
Premiums earned related to insurance business	652	656	1,302	1,309
Insurance underwriting income (loss)	160	140	287	222
Property and Casualty Insurance [Member]
Revenues
Investment Income	328	345	660	696
Total Revenues	3,461	3,409	6,898	6,789
Investment income	318	336	$ 639	677
Other charges	$ (7)	$ (2)		$ (4)

Represents income (loss) before income tax related to non-insurance companies before realized investment gain (loss).

No definition available.

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Represents revenues related to non-insurance companies, before realized investment gains or losses.

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Other income loss

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No definition available.

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- Definition

Premiums recognized as revenue in the period earned on all property and casualty insurance and reinsurance contracts after subtracting any amounts ceded to another insurer and before reinsurance assumed business which is in run-off.

+ References

No definition available.

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Premiums recognized as revenue in the period earned on property and casualty reinsurance assumed business which is in run-off.

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No definition available.

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- Definition

Amount of income (loss) before income tax for property and casualty insurance including underwriting income (loss), investment income (loss) and other income (charges), before realized investment gain (loss).

+ References

No definition available.

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Amount of underwriting income (loss) for the reportable property and casualty insurance segments which is arrived at by reducing premiums earned by losses and loss expenses incurred and statutory underwriting expenses incurred, before reinsurance assumed business which is in run-off. Under statutory accounting principles, policy acquisition and other underwriting expenses are recognized immediately, not at the time premiums are earned.

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No definition available.

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Amount of underwriting income (loss) for the property and casualty insurance reinsurance assumed segment, which is in run-off, which is arrived at by reducing premiums earned by losses and loss expenses incurred and statutory underwriting expenses incurred. Under statutory accounting principles, policy acquisition and other underwriting expenses are recognized immediately, not at the time premiums are earned.

+ References

No definition available.

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The amount of property and casualty underwriting income (loss).

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The amount of property and casualty underwriting income (loss) before deferred acquisition costs.

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This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (c)-(e)

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.7(c),9(a))

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This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 20

-Section 25

-Paragraph 1

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-Name Accounting Standards Codification

-Topic 235

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 10

-Article 5

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- Definition

The increase (decrease) during the reporting period in the balance sheet value of capitalized sales costs that are associated with acquiring a new insurance customers.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

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Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.1-5)

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Amount, after premiums ceded to other entities and premiums assumed by the entity, of property and casualty premiums earned.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.1)

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-Topic 944

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

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-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

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