| **Reserves in Addition to Account Balance, Based on Expected No-Lapse Guarantee Benefits and Expected Policy Assessments (Detail) - USD ($) $ in Millions** | Sep. 30, 2015 | Dec. 31, 2014 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Liability for Future Policy Benefit, by Product Segment [Line Items]**                                                                                    |          |          |
| Life policy and investment contract reserves                                                                                                                | $ 2,564       | $ 2,497       |
| Ordinary/Traditional Life                                                                                                                                   |          |          |
| **Liability for Future Policy Benefit, by Product Segment [Line Items]**                                                                                    |          |          |
| Life policy and investment contract reserves                                                                                                                | 928           | 875           |
| Deferred Annuities                                                                                                                                          |          |          |
| **Liability for Future Policy Benefit, by Product Segment [Line Items]**                                                                                    |          |          |
| Life policy and investment contract reserves                                                                                                                | 864           | 863           |
| Universal Life                                                                                                                                              |          |          |
| **Liability for Future Policy Benefit, by Product Segment [Line Items]**                                                                                    |          |          |
| Life policy and investment contract reserves                                                                                                                | 547           | 530           |
| Structured Settlements                                                                                                                                      |          |          |
| **Liability for Future Policy Benefit, by Product Segment [Line Items]**                                                                                    |          |          |
| Life policy and investment contract reserves                                                                                                                | 177           | 182           |
| Other                                                                                                                                                       |          |          |
| **Liability for Future Policy Benefit, by Product Segment [Line Items]**                                                                                    |          |          |
| Life policy and investment contract reserves                                                                                                                | $ 48          | $ 47          |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accrued obligation to policyholders that relates to insured events under long-term life insurance contracts.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.13(a)(1)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 25 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=28366191&loc=d3e13145-158430Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 13 -Subparagraph a -Article 7
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