| **Investments (Narrative) (Details) (USD $)**                                                                                     | 12 Months Ended  |
|-----------------------------------------------------------------------------------------------------------------------------------|------------------|
||
| Fair value                                                                                                                        | $ 40,241,000,000 | $ 38,017,000,000 |   |
| Cost or Amortized Cost                                                                                                            | 37,633,000,000   | 36,849,000,000 |   |
| Gross Unrealized Losses                                                                                                           | 541,000,000      | 804,000,000 |   |
| Net unrealized gains (losses) related to changes in fair value of trading securities still held included in net investment income |        |    | (5,000,000) |
| Number of non-income producing fixed maturity securities                                                                          | 9                | 7 |   |
| Fair value of non income fixed maturity security                                                                                  | 3,000,000        | 3,000,000 |   |
| Number of investments that exceed ten percent of stockholders' equity                                                             |        |    |   |
| Net unrealized gains (losses) related to changes in the fair value of securities for which the fair value option has been elected | 2,000,000        | (1,000,000) |   |
| Limited partnership investments                                                                                                   | 2,245,000,000    | 2,309,000,000 |   |
| Undistributed earnings of limited partnership investments                                                                         | 560,000,000      | 723,000,000 |   |
| Percentage of limited partnerships reported on a current basis                                                                    | 58.00%           |   |   |
| Percentage of limited partnerships reported on a one month lag                                                                    | 25.00%           |   |   |
| Number of active limited partnership investments held                                                                             | 79               | 75 |   |
| Percentage of limited partnerships employing hedge fund strategies focused on fixed income and equity investments                 | 81.00%           | 85.00% |   |
| Percentage of equity related limited partnership hedge fund strategies                                                            | 46.00%           |   |   |
| Percentage of multistrategy approach limited partnership hedge fund strategies                                                    | 32.00%           |   |   |
| Percentage of distressed investments limited partnership hedge fund strategies                                                    | 19.00%           |   |   |
| Percentage of fixed income limited partnership hedge fund strategies                                                              | 3.00%            |   |   |
| Limited partnerships invested in private equity                                                                                   | 14.00%           | 11.00% |   |
| Carrying value of ten largest limited partnerships                                                                                | 1,218,000,000    | 1,321,000,000 |   |
| Carrying value of limited partnerships as percentage of aggregate partnership equity                                              | 4.00%            |   |   |
| Income as percentage of change in partnership equity for all limited partnerships                                                 | 4.00%            | 3.00% | 4.00% |
| Commitments to purchase various privately placed debt securities                                                                  | 95,000,000       |   |   |
| Commitments to sell various privately placed debt securities                                                                      | 69,000,000       |   |   |
| Obligations on Unfunded Bank Loan Participations                                                                                  | 6,000,000        |   |   |
| Mortgage loan commitments                                                                                                         | 48,000,000       |   |   |
| Carrying value of securities deposited under requirements of regulatory authorities                                               | 3,500,000,000    | 2,900,000,000 |   |
| Cash and securities deposited as collateral for letters of credit                                                                 | 5,000,000        | 6,000,000 |   |
| Carrying value of assets deposited to secure reinsurance and third party obligations                                              | 288,000,000      | 298,000,000 |   |
| Corporate and other bonds, financial industry sector [Member]                                                                     |             |   |   |
| Fair value                                                                                                                        | 1,682,000,000    |   |   |
| Cost or Amortized Cost                                                                                                            | 1,788,000,000    |   |   |
| States, municipalities and political subdivisions [Member]                                                                        |             |   |   |
| Fair value                                                                                                                        | 9,782,000,000    | 7,889,000,000 |   |
| Cost or Amortized Cost                                                                                                            | 9,018,000,000    | 8,157,000,000 |   |
| Gross Unrealized Losses                                                                                                           | 136,000,000      | 410,000,000 |   |
| Percentage of gross unrealized losses by AA or higher securities                                                                  | 83.00%           |   |   |
| Gross unrealized losses of largest exposure, Puerto Rico sales tax revenue bonds                                                  | 80,000,000       |   |   |
| Asset-backed [Member]                                                                                                             |             |   |   |
| Fair value                                                                                                                        | 8,084,000,000    | 7,846,000,000 |   |
| Cost or Amortized Cost                                                                                                            | 8,097,000,000    | 8,001,000,000 |   |
| Gross Unrealized Losses                                                                                                           | 246,000,000      | 314,000,000 |   |
| Number of different asset backed securities comprising total fair value of asset backed securities                                | 2,010            |   |   |
| Number of securities with sub-prime and alt-a exposure                                                                            | 112              |   |   |
| Mortgage backed securities, issued by U.S. Government sponsored enterprises [Member]                                              |             |   |   |
| Gross Unrealized Losses                                                                                                           | 35,000,000       |   |   |
| Non-agency structured residential mortgage backed securities [Member]                                                             |             |   |   |
| Gross Unrealized Losses                                                                                                           | 148,000,000      |   |   |
| Number of securities with at least one trade lot in a gross unrealized loss position                                              | 131              |   |   |
| Severity of gross unrealized loss as percentage of amortized cost                                                                 | 11.00%           |   |   |
| Commercial mortgage-backed [Member]                                                                                               |             |   |   |
| Fair value                                                                                                                        | 1,354,000,000    | 993,000,000 |   |
| Cost or Amortized Cost                                                                                                            | 1,365,000,000    | 994,000,000 |   |
| Gross Unrealized Losses                                                                                                           | 59,000,000       | 41,000,000 |   |
| Number of securities with at least one trade lot in a gross unrealized loss position                                              | 61               |   |   |
| Severity of gross unrealized loss as percentage of amortized cost                                                                 | 9.00%            |   |   |
| Other asset-backed [Member]                                                                                                       |             |   |   |
| Fair value                                                                                                                        | 955,000,000      | 763,000,000 |   |
| Cost or Amortized Cost                                                                                                            | 946,000,000      | 753,000,000 |   |
| Gross Unrealized Losses                                                                                                           | 4,000,000        | 8,000,000 |   |
| Number of securities with at least one trade lot in a gross unrealized loss position                                              | 51               |   |   |
| Severity of gross unrealized loss as percentage of amortized cost                                                                 | 1.00%            |   |   |
| Mortgage loans [Member]                                                                                                           |             |   |   |
| Percentage of the carrying value of commercial mortgage loans related to credit tenant loans                                      | 14.00%           | 40.00% |   |
| Commercial mortgage loans past due or in non-accrual status                                                                       |        |    |   |
| Valuation allowances recorded on commercial mortgage loans                                                                        |        |    |   |
| Investment commitment [Member]                                                                                                    |             |   |   |
| Future capital call commitments                                                                                                   | $ 129,000,000    |   |   |

| X                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Carrying Value of Assets Deposited to Secure Reinsurance and Third Party Obligations
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Carrying value Of Limited Partnerships As Percentage of Aggregate Partnership Equity
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Carrying Value Of Securities Deposited Under Requirements Of Regulatory Authorities
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Carrying Value Of Ten Largest Limited Partnerships
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| - Definition
Cash And Securities Deposited As Collateral For Letters Of Credit
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Commitments To Purchase Various Privately Placed Debt Securities
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| - Definition
Commitments To Sell Various Privately Placed Debt Securities
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| X                                                                                                                                                                                                                                                                             |
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| - Definition
Fair Value Of Non Income Fixed Maturity Security
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| X                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Future capital call commitments to third party limited partnerships for which we would receive an ownership interest.
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| - Definition
Gross unrealized losses of largest exposure, Puerto Rico sales tax revenue bonds
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| - Definition
Income As Percentage Of Change In Partnership Equity For All Limited Partnerships
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No definition available.
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| - Definition
This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee.
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| - Definition
Limited Partnerships Invested In Private Equity
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| X                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Mortgage loan commitments, representing signed loan applications received and accepted.
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| X                                                                                                                                                                                                                                                                                    |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Number of active limited partnership investments held
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| - Definition
Number Of Different Asset Backed Securities Comprising Total Fair Value Of Asset backed Holdings
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Number of Investments that Exceed Ten Percent of Stockholders' Equity, other than investments in U.S. Treasury and U.S. Government agency securities.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Number of Non-Income Producing Fixed Maturity Securities
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| X                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Number of securities with sub-prime and alt-a exposure
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| X                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Obligations on Unfunded Bank Loan Participations
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| - Definition
Percentage of the Carrying Value of Commercial Mortgage Loans Related to Credit Tenant Loans
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of Distressed Investments Limited Partnership Hedge Fund Strategies
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of Equity Related Limited Partnership Hedge Fund Strategies
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of Fixed Income Limited Partnership Hedge Fund Strategies
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No definition available.
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of gross unrealized losses by AA or higher securities
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of limited partnerships employing hedge fund strategies focused on fixed income and equity investments
+ References
No definition available.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of total carrying value of limited partnerships reported on a current basis
+ References
No definition available.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of total carrying value of limited partnerships reported on a one month lag.
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No definition available.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of Multistrategy Approach Limited Partnership Hedge Fund Strategies
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Severity of Gross Unrealized Loss as Percentage of Amortized Cost
+ References
No definition available.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS115-1/124-1 -Paragraph 7 -Footnote 2 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 19 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 12 -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6379932&loc=d3e22054-111558Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Available-for-Sale Securities -URI http://asc.fasb.org/extlink&oid=6505594
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the gross unrealized losses for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.
+ References
No definition available.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the available-for-sale investments determined to be temporarily impaired.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 03-1 -Paragraph 21 -Subparagraph b(3) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS115-1/124-1 -Paragraph 17 -Subparagraph b(3) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27290-111563
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents, for each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings during the period and in which line in the income statement those gains and losses are reported. This item may also include amounts of gains and losses for other items measured at fair value, but for which the fair value option has not been elected (for instance, items required to be measured at fair value).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 159 -Paragraph 19 -Subparagraph a -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 30 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14172-108612
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
A valuation allowance for financing receivables that are expected to be uncollectible.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -URI http://asc.fasb.org/extlink&oid=6965416&loc=SL6953423-111524 -Subparagraph (c)(1)
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Recorded Investment in financing receivables that are past due at the balance sheet date.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of consolidated retained earnings that represent undistributed (not yet received) earnings from 50% or less owned persons accounted for by the equity method (equity method investees).
+ References
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| - Definition
The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of trading securities held at each balance sheet date, that was included in earnings for the period. Trading securities are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) and the change in net unrealized holding gain (loss) is included in earnings for the period.
+ References
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