Federal and Foreign Income Tax - Tax Effects of Temporary Differences that Gave Rise to Deferred Income Tax Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred income tax assets
Unpaid losses and loss expenses	$ 605	$ 632
Unearned premiums	341	339
Foreign tax credits	870	853
Employee compensation	119	116
Postretirement benefits	324	293
Other-than-temporary impairment losses	294	286
Total deferred income tax assets	2,553	2,519
Deferred income tax liabilities
Deferred policy acquisition costs	341	341
Unremitted earnings of foreign subsidiaries	951	894
Unrealized appreciation of investments	1,084	934
Other invested assets	225	235
Other, net	114	117
Total deferred income tax liabilities	2,715	2,521
Net deferred income tax liability	$ 162	$ 2