Investments (Credit Ratings Of Asset-Backed And Mortgage-Backed Securities And Corporate Obligations In Available-For-Sale Investments For Which Fair Value Was Less Than Amortized Cost) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule Of Available For Sale Securities [Line Items]
Fair value	$ 2,893	$ 1,284
Unrealized Loss	(195)	(152)
Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	223
Unrealized Loss	(78)
Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	639
Unrealized Loss	(28)
Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	566
Unrealized Loss	(38)
Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	1,428
Unrealized Loss	(144)
Moodys Aaa Rating [Member] \| Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	14
Unrealized Loss	0
Moodys Aaa Rating [Member] \| Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	589
Unrealized Loss	(21)
Moodys Aaa Rating [Member] \| Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	47
Unrealized Loss	(1)
Moodys Aaa Rating [Member] \| Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	650
Unrealized Loss	(22)
Moodys Aa 1 Rating [Member] \| Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	62
Unrealized Loss	(5)
Moodys Aa 1 Rating [Member] \| Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	6
Unrealized Loss	0
Moodys Aa 1 Rating [Member] \| Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	164
Unrealized Loss	(7)
Moodys Aa 1 Rating [Member] \| Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	232
Unrealized Loss	(12)
Moodys A 1 Rating [Member] \| Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	3
Unrealized Loss	0
Moodys A 1 Rating [Member] \| Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	7
Unrealized Loss	0
Moodys A 1 Rating [Member] \| Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	238
Unrealized Loss	(13)
Moodys A 1 Rating [Member] \| Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	248
Unrealized Loss	(13)
Moodys Baa 1 Rating [Member] \| Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	4
Unrealized Loss	0
Moodys Baa 1 Rating [Member] \| Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	17
Unrealized Loss	(1)
Moodys Baa 1 Rating [Member] \| Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	99
Unrealized Loss	(16)
Moodys Baa 1 Rating [Member] \| Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	120
Unrealized Loss	(17)
Below Investment Grade [Member] \| Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	140
Unrealized Loss	(73)
Below Investment Grade [Member] \| Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	5
Unrealized Loss	(1)
Below Investment Grade [Member] \| Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	18
Unrealized Loss	(1)
Below Investment Grade [Member] \| Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	163
Unrealized Loss	(75)
Not Rated [Member] \| Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	0
Unrealized Loss	0
Not Rated [Member] \| Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	15
Unrealized Loss	(5)
Not Rated [Member] \| Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	0
Unrealized Loss	0
Not Rated [Member] \| Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	15
Unrealized Loss	$ (5)

Investments (Credit Ratings Of Asset-Backed And Mortgage-Backed Securities And Corporate Obligations In Available-For-Sale Investments For Which Fair Value Was Less Than Amortized Cost) (Detail) (USD $)
In Millions, unless otherwise specified