Investments (Fair Values And Gross Unrealized Losses By Credit Rating Category Of ABS, MBS And Corporate Obligations) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	$ 1,130
Total, Unrealized Losses	(126)
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	227
Total, Unrealized Losses	(82)
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	551
Total, Unrealized Losses	(18)
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	352
Total, Unrealized Losses	(26)
Aaa [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	469
Total, Unrealized Losses	(5)
Aaa [Member] | Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	25
Total, Unrealized Losses	(1)
Aaa [Member] | Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	439
Total, Unrealized Losses	(4)
Aaa [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	5
Aa [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	140
Total, Unrealized Losses	(6)
Aa [Member] | Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	64
Total, Unrealized Losses	(5)
Aa [Member] | Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	4
Aa [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	72
Total, Unrealized Losses	(1)
A1 [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	277
Total, Unrealized Losses	(18)
A1 [Member] | Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	3
A1 [Member] | Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	78
Total, Unrealized Losses	(7)
A1 [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	196
Total, Unrealized Losses	(11)
Baa [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	68
Total, Unrealized Losses	(13)
Baa [Member] | Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	1
Baa [Member] | Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	2
Baa [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	65
Total, Unrealized Losses	(13)
Below Investment Grade [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	161
Total, Unrealized Losses	(79)
Below Investment Grade [Member] | Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	134
Total, Unrealized Losses	(76)
Below Investment Grade [Member] | Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	13
Total, Unrealized Losses	(2)
Below Investment Grade [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	14
Total, Unrealized Losses	(1)
Not Rated [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	15
Total, Unrealized Losses	(5)
Not Rated [Member] | Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value
Total, Unrealized Losses
Not Rated [Member] | Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	15
Total, Unrealized Losses	(5)
Not Rated [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value
Total, Unrealized Losses