Reinsurance (Assumed Life Reinsurance Programs Involving Minimum Benefit Guarantees Under Annuity Contracts - Narrative) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Guaranteed Minimum Death Benefit	Dec. 31, 2011 Guaranteed Minimum Death Benefit	Dec. 31, 2012 Guaranteed Minimum Deaths Benefits And Guaranteed Living Benefits [Member]	Dec. 31, 2011 Guaranteed Minimum Deaths Benefits And Guaranteed Living Benefits [Member]	Dec. 31, 2012 Guaranteed Living Benefits [Member]	Dec. 31, 2011 Guaranteed Living Benefits [Member]	Dec. 31, 2010 Guaranteed Living Benefits [Member]	Dec. 31, 2009 Guaranteed Living Benefits [Member]
Guaranteed Minimum Benefits [Line Items]
Reinsurance recoveries on losses and loss expenses incurred	$ 4,300,000,000	$ 3,300,000,000	$ 3,300,000,000
Provision for uncollectible reinsurance	439,000,000	479,000,000
Reported liabilities				90,000,000	138,000,000			1,400,000,000	1,500,000,000	648,000,000	559,000,000
Fair value derivative adjustment in liability								1,100,000,000	1,300,000,000
Net amount at risk				1,300,000,000	1,800,000,000			445,000,000	380,000,000
Mortality percentage according to Annuity 2000 mortality table						100.00%
Discounting assumption used in the calculation of the benefit reserve averaging - lower range				1.00%		1.50%		3.50%
Discounting assumption used in the calculation of the benefit reserve averaging - upper range				2.00%		2.50%		4.50%
Total claim amount payable, if all of the Company's cedants' policyholders covered were to die immediately				495,000,000		640,000,000
GMBD net amount of risk						116,000,000	182,000,000
GLB net amount of risk						$ 655,000,000	$ 998,000,000
Average attained age of all policyholders under all benefits reinsured, years	68 years