Reinsurance (Assumed Life Reinsurance Programs Involving Minimum Benefit Guarantees Under Annuity Contracts - Narrative) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Guaranteed Minimum Benefits [Line Items]
Reinsurance recoveries on losses and loss expenses incurred	$ 3,100,000,000	$ 3,100,000,000	$ 4,300,000,000
Provision for uncollectible reinsurance	357,000,000	390,000,000
Average attained age of all policyholders under all benefits reinsured, years	69 years
Guaranteed Minimum Death Benefit
Guaranteed Minimum Benefits [Line Items]
Reported liabilities	111,000,000	100,000,000
Discount rate - lower range	2.50%
Discount rate - upper range	3.50%
Guaranteed Minimum Deaths Benefits And Guaranteed Living Benefits [Member]
Guaranteed Minimum Benefits [Line Items]
Mortality percentage according to Annuity 2000 mortality table	100.00%
Discount rate - lower range	3.50%
Discount rate - upper range	4.50%
Guaranteed Living Benefits [Member]
Guaranteed Minimum Benefits [Line Items]
Reported liabilities	663,000,000	427,000,000	1,400,000,000	1,500,000,000
Fair value derivative adjustment in liability	$ 406,000,000	$ 193,000,000
Discount rate - lower range	3.50%
Discount rate - upper range	4.50%