Earned Consolidated Property Casualty Insurance Premiums on Assumed and Ceded Business (Detail) (USD $) In Millions	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Direct earned premiums	$ 817	$ 782	$ 2,404	$ 2,295
Assumed earned premiums	3	3	10	8
Ceded earned premiums	(51)	(42)	(170)	(124)
Net earned premiums	$ 769	$ 743	$ 2,244	$ 2,179

Premiums assumed and earned for all property and casualty insurance assumed from other insurers as a result of reinsurance arrangements.

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Premiums assumed and earned by another insurer as a result of reinsurance arrangements.

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Premiums earned directly for all property and casualty insurance before adding contracts assumed from other insurers or subtracting any amounts assumed by other insurers.

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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.

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