| **Accumulated Other Comprehensive Income (Loss) by Component (Schedule of accumulated other comprehensive income (loss) by component) (Details) - USD ($) $ in Millions** | 3 Months Ended |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|
||
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                                |           |   |
| Total stockholder's equity at beginning of period                                                                                                                         | $ 12,809       |   |
| Other comprehensive income (loss) before reclassifications                                                                                                                | (1,630)        | $ (594) |
| Amounts reclassified from accumulated other comprehensive income (loss) net of tax                                                                                        | (7)            | 22 |
| Other comprehensive income (loss) after tax (expense) benefit                                                                                                             | (1,623)        | (616) |
| Total stockholder's equity at end of period                                                                                                                               | 10,817         | 12,089 |
| Reclassification from AOCI, tax                                                                                                                                           | 3              | (5) |
| Tax (expense) benefit on other comprehensive income (loss)                                                                                                                | 423            | 160 |
| Accumulated other comprehensive income (loss)                                                                                                                             |           |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                                |           |   |
| Total stockholder's equity at beginning of period                                                                                                                         | 320            | 803 |
| Total stockholder's equity at end of period                                                                                                                               | (1,303)        | 187 |
| Net unrealized gains (losses) on investments with an allowance for credit losses                                                                                          |           |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                                |           |   |
| Total stockholder's equity at beginning of period                                                                                                                         |           | 0 |
| Other comprehensive income (loss) before reclassifications                                                                                                                |           | (3) |
| Amounts reclassified from accumulated other comprehensive income (loss) net of tax                                                                                        |           | (3) |
| Other comprehensive income (loss) after tax (expense) benefit                                                                                                             |           | 0 |
| Total stockholder's equity at end of period                                                                                                                               |           | 0 |
| Net unrealized gains (losses) on investments with an allowance for credit losses | Net unrealized gains (losses) on investments with an allowance for credit losses       |           |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                                |           |   |
| Total stockholder's equity at beginning of period                                                                                                                         | (2)            |   |
| Other comprehensive income (loss) before reclassifications                                                                                                                | (4)            |   |
| Amounts reclassified from accumulated other comprehensive income (loss) net of tax                                                                                        | 0              |   |
| Other comprehensive income (loss) after tax (expense) benefit                                                                                                             | (4)            |   |
| Total stockholder's equity at end of period                                                                                                                               | (6)            |   |
| Reclassification from AOCI, tax                                                                                                                                           |           | 1 |
| Tax (expense) benefit on other comprehensive income (loss)                                                                                                                |           | 0 |
| Net unrealized gains (losses) on investments                                                                                                                              |           |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                                |           |   |
| Total stockholder's equity at beginning of period                                                                                                                         |           | 1,745 |
| Other comprehensive income (loss) before reclassifications                                                                                                                |           | (593) |
| Amounts reclassified from accumulated other comprehensive income (loss) net of tax                                                                                        |           | 34 |
| Other comprehensive income (loss) after tax (expense) benefit                                                                                                             |           | (627) |
| Total stockholder's equity at end of period                                                                                                                               |           | 1,118 |
| Net unrealized gains (losses) on investments | Net unrealized gains (losses) on investments with an allowance for credit losses                                           |           |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                                |           |   |
| Reclassification from AOCI, tax                                                                                                                                           | 0              |   |
| Tax (expense) benefit on other comprehensive income (loss)                                                                                                                | 1              |   |
| Net unrealized gains (losses) on investments | Net unrealized gains (losses) on other investments                                                                         |           |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                                |           |   |
| Total stockholder's equity at beginning of period                                                                                                                         | 1,039          |   |
| Other comprehensive income (loss) before reclassifications                                                                                                                | (1,612)        |   |
| Amounts reclassified from accumulated other comprehensive income (loss) net of tax                                                                                        | (1)            |   |
| Other comprehensive income (loss) after tax (expense) benefit                                                                                                             | (1,611)        |   |
| Total stockholder's equity at end of period                                                                                                                               | (572)          |   |
| Reclassification from AOCI, tax                                                                                                                                           | 1              | (8) |
| Tax (expense) benefit on other comprehensive income (loss)                                                                                                                | 424            | 162 |
| Pension and postretirement benefits                                                                                                                                       |           |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                                |           |   |
| Total stockholder's equity at beginning of period                                                                                                                         | (604)          | (848) |
| Other comprehensive income (loss) before reclassifications                                                                                                                | 0              | 0 |
| Amounts reclassified from accumulated other comprehensive income (loss) net of tax                                                                                        | (6)            | (9) |
| Other comprehensive income (loss) after tax (expense) benefit                                                                                                             | 6              | 9 |
| Total stockholder's equity at end of period                                                                                                                               | (598)          | (839) |
| Reclassification from AOCI, tax                                                                                                                                           | 2              | 2 |
| Tax (expense) benefit on other comprehensive income (loss)                                                                                                                | (2)            | (2) |
| Cumulative foreign currency translation adjustment                                                                                                                        |           |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                                |           |   |
| Total stockholder's equity at beginning of period                                                                                                                         | (113)          | (94) |
| Other comprehensive income (loss) before reclassifications                                                                                                                | (14)           | 2 |
| Amounts reclassified from accumulated other comprehensive income (loss) net of tax                                                                                        | 0              | 0 |
| Other comprehensive income (loss) after tax (expense) benefit                                                                                                             | (14)           | 2 |
| Total stockholder's equity at end of period                                                                                                                               | (127)          | (92) |
| Reclassification from AOCI, tax                                                                                                                                           | 0              | 0 |
| Tax (expense) benefit on other comprehensive income (loss)                                                                                                                | $ 0            | $ 0 |

| X                                                                                                                                                                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.
+ References
No definition available.
+ Details**Name:**us-gaap_AOCIAttributableToParentNetOfTaxRollForward**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 55 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=124507222&loc=d3e1436-108581Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=124509347&loc=SL7669686-108580
+ Details**Name:**us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount after tax of other comprehensive income (loss) attributable to parent entity.
+ References
Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 1B -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=124509347&loc=SL7669625-108580Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=123454820&loc=SL4569643-111683Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 1A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=124509347&loc=SL7669619-108580Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 19 -URI http://asc.fasb.org/extlink&oid=123454820&loc=SL4569616-111683
+ Details**Name:**us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of tax expense (benefit) allocated to other comprehensive income (loss) attributable to parent entity.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=123454820&loc=SL4569643-111683Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 19 -URI http://asc.fasb.org/extlink&oid=123454820&loc=SL4569616-111683Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684
+ Details**Name:**us-gaap_OtherComprehensiveIncomeLossTaxPortionAttributableToParent1**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=124509347&loc=SL7669686-108580Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 55 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=124507222&loc=d3e1436-108581
+ Details**Name:**us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss).
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=124509347&loc=d3e640-108580Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=124431353&loc=SL124442407-227067Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 17A -URI http://asc.fasb.org/extlink&oid=124509347&loc=SL34724391-108580
+ Details**Name:**us-gaap_ReclassificationFromAociCurrentPeriodTax**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.
+ References
Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(g)(1)(ii)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 852 -SubTopic 10 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=84165509&loc=d3e56426-112766Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 4.E) -URI http://asc.fasb.org/extlink&oid=122038336&loc=d3e74512-122707Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(31)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(30)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 28 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=123596393&loc=d3e14064-108612Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571
+ Details**Name:**us-gaap_StockholdersEquity**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedOtherComprehensiveIncomeMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedOtherThanTemporaryImpairmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=us-gaap_InvestmentsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=us-gaap_OtherInvestmentsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                    |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedTranslationAdjustmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |