Investments (Average Credit Ratings And Fair Value And Percentage Of Guaranteed ABS MBS And Corporate Obligations Below Investment Grade) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 100
Percentage	64.00%
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	83
Percentage	95.00%
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value
Percentage