Assumed Life Reinsurance Programs Involving Minimum Benefit Guarantees Under Annuity Contracts (Narrative) (Detail) (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013 Guaranteed Minimum Death Benefit [Member]	Dec. 31, 2012 Guaranteed Minimum Death Benefit [Member]	Sep. 30, 2013 Guaranteed Minimum Income Benefit [Member]	Dec. 31, 2012 Guaranteed Minimum Income Benefit [Member]	Sep. 30, 2012 Guaranteed Minimum Income Benefit [Member]	Jun. 30, 2012 Guaranteed Minimum Income Benefit [Member]	Dec. 31, 2011 Guaranteed Minimum Income Benefit [Member]	Sep. 30, 2013 Guaranteed Minimum Deaths Benefits And Guaranteed Living Benefits [Member]	Dec. 31, 2012 Guaranteed Minimum Deaths Benefits And Guaranteed Living Benefits [Member]	Sep. 30, 2013 Guaranteed Living Benefits [Member]	Dec. 31, 2012 Guaranteed Living Benefits [Member]
Guaranteed Minimum Benefits [Line Items]
Reported liabilities		$ 95,000,000	$ 90,000,000	$ 746,000,000	$ 1,400,000,000	$ 1,500,000,000	$ 1,600,000,000	$ 1,500,000,000
Fair value derivative adjustment in liability				514,000,000	1,100,000,000
Net amount at risk		751,000,000	1,300,000,000								220,000,000	445,000,000
Mortality percentage according to Annuity 2000 mortality table											100.00%
Discounting assumption used in the calculation of the benefit reserve averaging - lower range		1.50%							2.50%		3.50%
Discounting assumption used in the calculation of the benefit reserve averaging - upper range		2.50%							3.50%		4.50%
Total claim amount payable, if all of the Company's cedants' policyholders covered were to die immediately		618,000,000							199,000,000
GMBD net amount of risk									85,000,000	116,000,000
GLB net amount of risk									$ 241,000,000	$ 655,000,000
Average attained age of all policyholders under all benefits reinsured, years	68 years