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Acquisitions and Sale of Businesses (Details Textual) - USD ($) $ in Millions |  |  | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Apr. 01, 2014 | Mar. 27, 2014 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Sep. 30, 2015 | Dec. 31, 2014 | Sep. 30, 2014 | Dec. 31, 2014
Acquisitions and Sale of Businesses [Line Items] |  |  |  |  |  |  |  |  |
Payments to acquire business |  |  |  |  |  | $ 0 |  | $ 267 |
Run-off long-term care insurance business [Member] |  |  |  |  |  |  |  |  |
Acquisitions and Sale of Businesses [Line Items] |  |  |  |  |  |  |  |  |
Sale proceeds |  |  |  | $ 7 |  |  |  |  |
Additional sale proceeds based on the release of certain statutory liabilities of the legal entities sold |  |  |  |  |  | $ 13 |  |  |
Carrying value of the assets and liabilities of business sold as a percentage of total assets and liabilities |  |  |  |  | 4.00% | 4.00% |  |  |
Summit Holding Southeast, Inc [Member] |  |  |  |  |  |  |  |  |
Acquisitions and Sale of Businesses [Line Items] |  |  |  |  |  |  |  |  |
Payments to acquire business | $ 259 |  |  |  |  |  |  |  |
Capital contributions to acquired business | 140 |  |  |  |  |  |  |  |
Total capital investment in acquired business | 399 |  |  |  |  |  |  |  |
Net written premiums of acquired business |  |  |  |  |  |  | $ 410 |  | $ 539
Net earned premiums of acquired business |  |  | $ 128 |  |  | $ 386 |  |  |
Selective Insurance Company of America Self-Insured Pooled Group [Member] |  |  |  |  |  |  |  |  |
Acquisitions and Sale of Businesses [Line Items] |  |  |  |  |  |  |  |  |
Payments to acquire business |  | $ 8 |  |  |  |  |  |  |
Net written premiums of acquired business |  |  |  |  |  |  |  |  | 23
In-force gross written premiums of acquired book of business |  | $ 38 |  |  |  |  |  |  |
Gross written premiums of acquired business |  |  |  |  |  |  |  |  | $ 33
Minimum [Member] | Run-off long-term care insurance business [Member] |  |  |  |  |  |  |  |  |
Acquisitions and Sale of Businesses [Line Items] |  |  |  |  |  |  |  |  |
Expected after-tax cash proceeds from the sale of business |  |  |  |  |  | 105 |  |  |
Maximum [Member] | Run-off long-term care insurance business [Member] |  |  |  |  |  |  |  |  |
Acquisitions and Sale of Businesses [Line Items] |  |  |  |  |  |  |  |  |
Expected after-tax cash proceeds from the sale of business |  |  |  |  |  | $ 115 |  |  |
Maximum [Member] | Summit Holding Southeast, Inc [Member] |  |  |  |  |  |  |  |  |
Acquisitions and Sale of Businesses [Line Items] |  |  |  |  |  |  |  |  |
Expenses related to the acquisition of business (are less than) | $ 1 |  |  |  |  |  |  |  |

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