Assumed Life Reinsurance Programs Involving Minimum Benefit Guarantees Under Annuity Contracts (Narrative) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Guaranteed Minimum Death Benefit [Member]	Dec. 31, 2012 Guaranteed Minimum Death Benefit [Member]	Mar. 31, 2013 Guaranteed Minimum Income Benefit [Member]	Dec. 31, 2012 Guaranteed Minimum Income Benefit [Member]	Mar. 31, 2012 Guaranteed Minimum Income Benefit [Member]	Dec. 31, 2011 Guaranteed Minimum Income Benefit [Member]	Mar. 31, 2013 Guaranteed Minimum Deaths Benefits And Guaranteed Living Benefits [Member]	Dec. 31, 2012 Guaranteed Minimum Deaths Benefits And Guaranteed Living Benefits [Member]	Mar. 31, 2013 Guaranteed Living Benefits [Member]	Dec. 31, 2012 Guaranteed Living Benefits [Member]	Mar. 31, 2013 Minimum [Member] Guaranteed Minimum Death Benefit [Member]	Mar. 31, 2013 Maximum [Member] Guaranteed Minimum Death Benefit [Member]
Guaranteed Minimum Benefits [Line Items]
Document Period End Date	Mar. 31, 2013
Reported liabilities			$ 89,000,000	$ 90,000,000	$ 1,000,000,000	$ 1,400,000,000	$ 1,050,000,000	$ 1,500,000,000
Fair value derivative adjustment in liability	753	1,100,000,000
Net amount at risk			1,000,000,000	1,300,000,000							345,000,000	445,000,000
Mortality percentage according to Annuity 2000 mortality table			100.00%
Percent of Annuity 2000 mortality table used for mortality assumption													1.00%	2.00%
Discounting assumption used in the calculation of the benefit reserve averaging - lower range									2.00%		3.50%
Discounting assumption used in the calculation of the benefit reserve averaging - upper range									3.00%		4.50%
Total claim amount payable, if all of the Company's cedants' policyholders covered were to die immediately			574,000,000						334,000,000
GMBD net amount of risk									93,000,000	116,000,000
GLB net amount of risk									$ 376,000,000	$ 655,000,000
Average attained age of all policyholders under all benefits reinsured, years	68 years