| **Stockholders' Equity and Statutory Accounting Practices Combined statutory capital and surplus and net income (loss) (Details) (USD $)In Millions, unless otherwise specified**                                | 12 Months Ended |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------|
||
| Combined Continental Casualty Companies [Member]                                                                                                                                                                 |            |  |   |  |   |  |
| **Statutory Accounting Practices [Line Items]**                                                                                                                                                                  |            |  |   |  |   |  |
| Statutory capital and surplus                                                                                                                                                                                    | $ 11,137        | [1],[2] | $ 9,998 | [1] |   |  |
| Statutory net income (loss)                                                                                                                                                                                      | 913             | [1],[2] | 391 | [1] | 954 | [1] |
| Life Company [Member]                                                                                                                                                                                            |            |  |   |  |   |  |
| **Statutory Accounting Practices [Line Items]**                                                                                                                                                                  |            |  |   |  |   |  |
| Statutory capital and surplus                                                                                                                                                                                    | 597             | [2] | 556 |  |   |  |
| Statutory net income (loss)                                                                                                                                                                                      | $ 48            | [2] | $ 44 |  | $ 29 |  |
|                                                                                                                                                                                                                  |
| [1]Represents the combined statutory surplus of CCC and its subsidiaries, including the life company.[2]Information derived from the statutory-basis financial statements to be filed with insurance regulators. |

| X                                                                                                                                                                         |
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.23(c)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 24 -Subparagraph c -Article 7
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of net income for the period determined using accounting principles prescribed or permitted by insurance regulators.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.23(c)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 24 -Subparagraph c -Article 7
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