Segments Information - Revenues, Income Before Income Tax and Assets of Each Operating Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues
Premiums earned related to insurance business									$ 12,069	$ 11,834	$ 11,631
Investment Income									1,465	1,556	1,644
Premiums earned related to reinsurance assumed									(3)	4	13
Net Premiums earned									12,066	11,838	11,644
Corporate and other									43	46	55
Realized investment gains, net									402	193	288
Total Revenues	3,476	3,403	3,551	3,517	3,400	3,362	3,423	3,410	13,947	13,595	13,585
Insurance underwriting income (loss)									1,607	498	475
Reinsurance assumed underwriting income									9	47	36
Underwriting income before deferred policy acquisition costs									1,616	545	511
Increase in deferred policy acquisition costs									59	3	63
Underwriting income									1,675	548	574
Investment income									1,416	1,518	1,605
Total property and casualty insurance									3,072	2,040	2,157
Corporate and other									(237)	(237)	(246)
Realized investment gains, net									402	193	288
INCOME BEFORE FEDERAL AND FOREIGN INCOME TAX									3,237	1,996	2,199
Assets
Total assets	50,433				52,184				50,433	52,184	50,445
Property and casualty insurance [Member]
Revenues
Investment Income									1,436	1,518	1,598
Total Revenues									13,502	13,356	13,242
Investment income									1,391	1,482	1,562
Other income									6	10	21
Operating Segments [Member]
Assets
Total assets	48,278				49,441				48,278	49,441	48,017
Operating Segments [Member] | Personal insurance [Member]
Revenues
Premiums earned related to insurance business									4,214	4,024	3,917
Insurance underwriting income (loss)									509	192	47
Operating Segments [Member] | Commercial insurance [Member]
Revenues
Premiums earned related to insurance business									5,237	5,144	4,945
Insurance underwriting income (loss)									692	44	1
Operating Segments [Member] | Specialty insurance [Member]
Revenues
Premiums earned related to insurance business									2,618	2,666	2,769
Insurance underwriting income (loss)									406	262	427
Corporate and other [Member]
Assets
Total assets	2,248				2,830				2,248	2,830	2,513
Adjustments and eliminations [Member]
Assets
Total assets	$ (93)				$ (87)				$ (93)	$ (87)	$ (85)