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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	Mar. 31, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Fair value	$ 1,206	$ 2,802
Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	240
Gross unrealized losses	(30)
Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	379
Gross unrealized losses	(11)
Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	386
Gross unrealized losses	(96)
Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	1,005
Gross unrealized losses	(137)
Moody's Aaa [Member] | Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	125
Gross unrealized losses	(1)
Moody's Aaa [Member] | Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	331
Gross unrealized losses	(4)
Moody's Aaa [Member] | Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	147
Gross unrealized losses	(1)
Moody's Aaa [Member] | Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	603
Gross unrealized losses	(6)
Moodys Aa 1 Rating [Member] | Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	74
Gross unrealized losses	(1)
Moodys Aa 1 Rating [Member] | Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	3
Gross unrealized losses	0
Moodys Aa 1 Rating [Member] | Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	109
Gross unrealized losses	0
Moodys Aa 1 Rating [Member] | Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	186
Gross unrealized losses	(1)
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	58
Gross unrealized losses	(1)
Moody's A1 [Member] | Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	62
Gross unrealized losses	(1)
Moody's Baa 1 Rating [Member] | Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	6
Gross unrealized losses	0
Moody's Baa 1 Rating [Member] | Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	5
Gross unrealized losses	0
Moody's Baa 1 Rating [Member] | Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	44
Gross unrealized losses	(3)
Moody's Baa 1 Rating [Member] | Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	55
Gross unrealized losses	(3)
Below Investment Grade [Member] | Asset-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	33
Gross unrealized losses	(28)
Below Investment Grade [Member] | Mortgage-backed [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	25
Gross unrealized losses	(3)
Below Investment Grade [Member] | Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	13
Gross unrealized losses	(3)
Below Investment Grade [Member] | Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	71
Gross unrealized losses	(34)
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	13
Gross unrealized losses	(4)
Not Rated [Member] | Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	15
Gross unrealized losses	(88)
Not Rated [Member] | Total ABS MBS and Corporate Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
Fair value	28
Gross unrealized losses	$ (92)

X

- Definition

Amount of accumulated pre-tax unrealized losses before deducting pre-tax unrealized gains on investments in available-for-sale securities impacting investments.

+ References

No definition available.

+ Details

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X

- Definition

This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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