Acquisitions (Details Textual) (USD $) In Millions, unless otherwise specified	9 Months Ended			0 Months Ended		6 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Mar. 27, 2014 Selective Insurance Company of America Self-Insured Pooled Group [Member]	Apr. 01, 2014 Summit Holding Southeast, Inc [Member]	Sep. 30, 2014 Summit Holding Southeast, Inc [Member]	Apr. 01, 2014 Summit Holding Southeast, Inc [Member]	Dec. 31, 2013 Minimum [Member] Summit Holding Southeast, Inc [Member]	Apr. 01, 2014 Maximum [Member] Summit Holding Southeast, Inc [Member]
Business Acquisition [Line Items]
Payments to acquire business	$ 267	$ 0		$ 8	$ 259
In-force gross written premiums of acquired book of business				38
Capital contributions to acquired business					140
Total capital investment in acquired business					399
Net written premiums of acquired business								500
Net earned premiums of acquired business						268
Expenses related to the acquisition of business (are less than)									1
Indefinite-lived intangible assets acquired							1
Finite-lived intangible assets acquired							46
Weighted average useful life of finite-lived intangible assets acquired					7 years
Goodwill	$ 201		$ 185				$ 16