Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash and cash equivalents
Cash and cash equivalents, maximum maturity at the date of purchase (in months)	3 months
Agent bonus estimates
Performance period for agent bonuses (in months)	36 months
Period of prior year actual underwriting data used to estimate agent bonuses (in years)	2 years
Property and Casualty Group
Deferred acquisition costs
Reduction to unamortized acquisition costs due to a premium deficiency when considering investment income	$ 0	$ 0	$ 0
Property and casualty unpaid losses and loss expenses
Interest rate used to discount workers compensation loss reserves (as a percent)	2.50%	2.50%	2.50%
Indemnity | Management operations
Recognition of management fee revenue
Indemnity's maximum management fee rate as a percent of premiums written and assumed by the Exchange (as a percent)	25.00%