Segments Information - Revenues of Property and Casualty Group by Geographic Area (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenues by geographic area
Revenues	$ 3,476	$ 3,574	$ 3,542	$ 3,506	$ 3,476	$ 3,403	$ 3,551	$ 3,517	$ 14,098	$ 13,947	$ 13,595
P&C Group [Member]
Revenues by geographic area
Revenues									13,696	13,502	13,356
Reportable Geographical Components [Member] | P&C Group [Member] | United States [Member]
Revenues by geographic area
Revenues									10,448	10,205	9,996
Reportable Geographical Components [Member] | P&C Group [Member] | International [Member]
Revenues by geographic area
Revenues									$ 3,248	$ 3,297	$ 3,360