Federal and Foreign Income Tax - Reconciliation of Effective Income Tax Rate and Statutory Federal Corporate Tax Rate (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income before federal and foreign income tax									$ 1,996	$ 2,199	$ 2,988
Tax at statutory federal income tax rate									699	770	1,046
Tax exempt interest income									(233)	(243)	(241)
Other, net									(15)	(6)	9
Federal and foreign income tax	$ (39)	$ 194	$ 123	$ 173	$ 150	$ 68	$ 127	$ 176	$ 451	$ 521	$ 814
Income before federal and foreign income tax, percentage of pre-tax income
Tax at statutory federal income tax rate, percentage of pre-tax income									35.00%	35.00%	35.00%
Tax exempt interest income, percentage of pre-tax income									(11.70%)	(11.00%)	(8.10%)
Other, net, percentage of pre-tax income									(0.70%)	(0.30%)	0.30%
Actual tax, percentage of pre-tax income									22.60%	23.70%	27.20%