Assumed Life Reinsurance Programs Involving Minimum Benefit Guarantees Under Annuity Contracts (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Guaranteed Minimum Benefits [Line Items]
Document Fiscal Year Focus	2015
Guaranteed Minimum Death Benefit [Member]
Guaranteed Minimum Benefits [Line Items]
Reported liabilities	112	$ 111
Guaranteed Living Benefit [Member]
Guaranteed Minimum Benefits [Line Items]
Reported liabilities	716	663	483	427
Fair value derivative adjustment in liability	451	$ 406