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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 | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | ---
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | $ 2,802 | $ 2,071
Asset-backed [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 307 |
Gross unrealized losses | (35) |
Mortgage-backed [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 625 |
Gross unrealized losses | (15) |
Corporate Obligations [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 771 |
Gross unrealized losses | (103) |
Total ABS MBS and Corporate Obligations [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 1,703 |
Gross unrealized losses | (153) |
Moody's Aaa [Member] | Asset-backed [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 182 |
Gross unrealized losses | (1) |
Moody's Aaa [Member] | Mortgage-backed [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 560 |
Gross unrealized losses | (9) |
Moody's Aaa [Member] | Corporate Obligations [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 117 |
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 | 859 |
Gross unrealized losses | (11) |
Moodys Aa 1 Rating [Member] | Asset-backed [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 82 |
Gross unrealized losses | (1) |
Moodys Aa 1 Rating [Member] | Mortgage-backed [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 17 |
Gross unrealized losses | 0 |
Moodys Aa 1 Rating [Member] | Corporate Obligations [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 235 |
Gross unrealized losses | (3) |
Moodys Aa 1 Rating [Member] | Total ABS MBS and Corporate Obligations [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 334 |
Gross unrealized losses | (4) |
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 | 313 |
Gross unrealized losses | (5) |
Moody's A1 [Member] | Total ABS MBS and Corporate Obligations [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 317 |
Gross unrealized losses | (5) |
Moody's Baa 1 Rating [Member] | Asset-backed [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 5 |
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 | 84 |
Gross unrealized losses | (8) |
Moody's Baa 1 Rating [Member] | Total ABS MBS and Corporate Obligations [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 94 |
Gross unrealized losses | (8) |
Below Investment Grade [Member] | Asset-backed [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 29 |
Gross unrealized losses | (33) |
Below Investment Grade [Member] | Mortgage-backed [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 26 |
Gross unrealized losses | (2) |
Below Investment Grade [Member] | Corporate Obligations [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 5 |
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 | 60 |
Gross unrealized losses | (35) |
Not Rated [Member] | Asset-backed [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 7 |
Gross unrealized losses | 0 |
Not Rated [Member] | Mortgage-backed [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 15 |
Gross unrealized losses | (4) |
Not Rated [Member] | Corporate Obligations [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 17 |
Gross unrealized losses | (86) |
Not Rated [Member] | Total ABS MBS and Corporate Obligations [Member] |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Fair value | 39 |
Gross unrealized losses | $ (90) |

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- 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 + Details
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