Shareholders' Equity - Comparison of Shareholders' Equity on Gaap Basis and Policyholders' Surplus on Statutory Basis (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010
Comparison of shareholders' equity on a GAAP basis and policyholders' surplus on a statutory basis
Shareholders' equity	$ 15,827	$ 15,301	[1]	$ 15,257	[1]
P&C Group [Member]
Comparison of shareholders' equity on a GAAP basis and policyholders' surplus on a statutory basis
Shareholders' equity	16,833	16,613
Policyholders' surplus	14,117	13,958
Corporate and Other [Member]
Comparison of shareholders' equity on a GAAP basis and policyholders' surplus on a statutory basis
Shareholders' equity	$ (1,006)	$ (1,312)

[1] As Adjusted