Acquisitions and Sale of Businesses (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended		0 Months Ended	9 Months Ended	12 Months Ended	0 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Apr. 01, 2014	Dec. 31, 2014	Dec. 31, 2014	Mar. 27, 2014
Acquisitions and Sale of Businesses [Line Items]
Payments to acquire business	$ 0	$ 8
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%
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	129
Underwriting profit of acquired business	5
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