Segments Information - Revenues and Income Before Income Tax of Each Operating Segment (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Revenues
Premiums earned related to insurance business	$ 3,166	$ 3,119	$ 9,405	$ 9,211
Premiums earned related to reinsurance assumed			(1)	1
Net Premiums earned	3,166	3,119	9,404	9,212
Investment Income	328	344	1,001	1,053
Corporate and other	8	7	25	25
Realized investment gains, net	82	110	113	351
Total Revenues	3,578	3,574	10,524	10,622
Insurance underwriting income (loss)	522	425	1,107	876
Reinsurance assumed underwriting income	4		7	1
Underwriting income before deferred policy acquisition costs	526	425	1,114	877
Increase (decrease) in deferred policy acquisition costs	(1)	14	44	48
Underwriting income	525	439	1,158	925
Total property and casualty insurance	831	766	2,103	1,925
Corporate and other	(66)	(58)	(209)	(177)
Realized investment gains, net	82	110	113	351
Income Before Federal and Foreign Income Tax	847	818	2,007	2,099
Personal Insurance [Member]
Revenues
Premiums earned related to insurance business	1,114	1,118	3,364	3,296
Insurance underwriting income (loss)	154	141	213	188
Commercial Insurance [Member]
Revenues
Premiums earned related to insurance business	1,390	1,338	4,077	3,943
Insurance underwriting income (loss)	207	151	446	333
Specialty Insurance [Member]
Revenues
Premiums earned related to insurance business	662	663	1,964	1,972
Insurance underwriting income (loss)	161	133	448	355
Property and Casualty Insurance [Member]
Revenues
Investment Income	322	338	982	1,034
Total Revenues	3,488	3,457	10,386	10,246
Investment income	310	$ 327	949	1,004
Other charges	$ (4)		$ (4)	$ (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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No definition available.

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- Definition

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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No definition available.

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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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-Topic 235

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-Section S99

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 10

-Article 5

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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

-SubTopic 605

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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

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-Topic 225

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-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

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