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, 2014	Dec. 31, 2013
Deferred income tax assets
Unpaid losses and loss expenses	$ 509	$ 524
Unearned premiums	364	350
Foreign tax credits	963	867
Employee compensation	144	142
Postretirement benefits	272	95
Other-than-temporary impairment losses	298	291
Other, net	29
Total deferred income tax assets	2,579	2,269
Deferred income tax liabilities
Deferred policy acquisition costs	367	356
Unremitted earnings of foreign subsidiaries	1,075	970
Unrealized appreciation of investments	944	660
Other invested assets	208	184
Other, net		52
Total deferred income tax liabilities	2,594	2,222
Net deferred income tax asset (liability)	$ (15)	$ 47