Acquisition (Details) (USD $)			0 Months Ended	12 Months Ended	0 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Oct. 07, 2011 White Mountains Holdings (Luxembourg)	Dec. 31, 2012 White Mountains Holdings (Luxembourg)	Oct. 07, 2011 Answer Financial Inc. company
Recorded amount of assets acquired
Cash paid on business acquisition			$ 1,010,000,000
Number of insurance companies for which comparison quotes for auto and homeowners insurance are offered					25
Present value of future profits			42,000,000
Goodwill	1,243,000,000	1,240,000,000	368,000,000
Other intangible assets			426,000,000
Reserve for property-liability claims and claims expense			487,000,000
Unearned premiums			229,000,000
Reduction in goodwill related to reestimates of opening balance sheet reserve for property-liability claims and claims expense				$ (2,000,000)