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	Sep. 30, 2014	Dec. 31, 2013
Schedule Of Available For Sale Securities [Line Items]
Fair value	$ 2,379	$ 3,457
Gross unrealized losses	(164)	(229)
Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	192
Gross unrealized losses	(35)
Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	530
Gross unrealized losses	(18)
Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	856
Gross unrealized losses	(91)
Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	1,578
Gross unrealized losses	(144)
Moody's Aaa [Member] \| Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	58
Gross unrealized losses	0
Moody's Aaa [Member] \| Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	496
Gross unrealized losses	(13)
Moody's Aaa [Member] \| Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	256
Gross unrealized losses	0
Moody's Aaa [Member] \| Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	810
Gross unrealized losses	(13)
Moodys Aa 1 Rating [Member] \| Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	60
Gross unrealized losses	(3)
Moodys Aa 1 Rating [Member] \| Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	6
Gross unrealized losses	0
Moodys Aa 1 Rating [Member] \| Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	218
Gross unrealized losses	(4)
Moodys Aa 1 Rating [Member] \| Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	284
Gross unrealized losses	(7)
Moody's A1 [Member] \| Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	2
Gross unrealized losses	0
Moody's A1 [Member] \| Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	2
Gross unrealized losses	0
Moody's A1 [Member] \| Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	295
Gross unrealized losses	(6)
Moody's A1 [Member] \| Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	299
Gross unrealized losses	(6)
Moody's Baa 1 Rating [Member] \| Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	2
Gross unrealized losses	0
Moody's Baa 1 Rating [Member] \| Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	3
Gross unrealized losses	0
Moody's Baa 1 Rating [Member] \| Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	55
Gross unrealized losses	(2)
Moody's Baa 1 Rating [Member] \| Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	60
Gross unrealized losses	(2)
Below Investment Grade [Member] \| Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	70
Gross unrealized losses	(32)
Below Investment Grade [Member] \| Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	9
Gross unrealized losses	(1)
Below Investment Grade [Member] \| Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	3
Gross unrealized losses	0
Below Investment Grade [Member] \| Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	82
Gross unrealized losses	(33)
Not Rated [Member] \| Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	0
Gross unrealized losses	0
Not Rated [Member] \| Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	14
Gross unrealized losses	(4)
Not Rated [Member] \| Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	29
Gross unrealized losses	(79)
Not Rated [Member] \| Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	43
Gross unrealized losses	$ (83)

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