Investments (Average Credit Ratings For Securities Rated Below Investment Grade Without The Effect Of Financial Guarantees) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Asset-backed [Member]
Schedule Of Investments [Line Items]
Fair Value Of Securities Rated Below Investment Grade Without Giving Effect To Benefit Of Guarantees Provided By Financial Guarantors	$ 101
Percentage Of Securities Rated Below Investment Grade Without Giving Effect To Benefit Of Guarantees Provided By Financial Guarantors	64.00%
Mortgage-backed [Member]
Schedule Of Investments [Line Items]
Fair Value Of Securities Rated Below Investment Grade Without Giving Effect To Benefit Of Guarantees Provided By Financial Guarantors	20
Percentage Of Securities Rated Below Investment Grade Without Giving Effect To Benefit Of Guarantees Provided By Financial Guarantors	99.00%
Corporate Obligations [Member]
Schedule Of Investments [Line Items]
Fair Value Of Securities Rated Below Investment Grade Without Giving Effect To Benefit Of Guarantees Provided By Financial Guarantors	$ 0
Percentage Of Securities Rated Below Investment Grade Without Giving Effect To Benefit Of Guarantees Provided By Financial Guarantors	0.00%