| **Life Policy and Investment Contract Reserves (Tables)**      | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                 |
|----------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Liability for Future Policy Benefits [Abstract]**            |                                                                                                                                                                                                                                                                                                                                                                                                                           |
| Reserve For Losses Loss Adjustment Expenses Table [Text Block] | This table summarizes our life policy and investment contract reserves:(In millions) June 30, 2014 December 31, 2013Ordinary/traditional life $848 $815Universal life 511 508Deferred annuities 865 862Structured settlements 184 189Other 46 16Total life policy and investment contract reserves $2,454 $2,390      |

| X                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Reserve for Losses Loss Adjustment Expenses [Table Text Block]
+ References
No definition available.
+ Details**Name:**cinf_ReserveForLossesLossAdjustmentExpensesTableTextBlock**Namespace Prefix:**cinf_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LiabilityForFuturePolicyBenefitsAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |