| **Reinsurance - Life Insurance Contract Holders' Benefits Incurred on Ceded Business (Detail) - USD ($) $ in Millions** | 3 Months Ended | 6 Months Ended |
|-------------------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]**                                       |           |           |   |   |
| Insurance losses and contract holders' benefits                                                                         | $ 821          | $ 712          | $ 1,545 | $ 1,461 |
| Life Insurance Segment                                                                                                  |           |           |   |   |
| **Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]**                                       |           |           |   |   |
| Direct contract holders' benefits incurred                                                                              | 80             | 72             | 156 | 144 |
| Ceded contract holders' benefits incurred                                                                               | (18)           | (14)           | (31) | (26) |
| Insurance losses and contract holders' benefits                                                                         | $ 62           | $ 58           | $ 125 | $ 118 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, before effect of policies assumed or ceded, of expense related to provision for policy benefits and costs incurred.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.5) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913
+ Details**Name:**us-gaap_PolicyholderBenefitsAndClaimsIncurredGross**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after effects of policies assumed or ceded, of expense related to the provision for policy benefits and costs incurred.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.5) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6811-158387
+ Details**Name:**us-gaap_PolicyholderBenefitsAndClaimsIncurredNet**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of reduction of provision for policy benefits and costs incurred for policies ceded.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6811-158387
+ Details**Name:**us-gaap_ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| 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.
+ Details**Name:**us-gaap_ReinsurancePremiumsForInsuranceCompaniesByProductSegmentLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementBusinessSegmentsAxis=us-gaap_LifeInsuranceSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |