Investments in Unconsolidated Affiliates (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Investments in unconsolidated affiliates
Investments in unconsolidated affiliates	$ 321.4		$ 387.9
Symetra
Investments in unconsolidated affiliates
Unrealized (losses) gains from Symetra’s fixed maturity portfolio	(43.6)		62.8
Investments in unconsolidated affiliates	317.3	[1],[2]	381.5	[3]	273.6	[3]	387.5
Symetra | Common Stock
Investments in unconsolidated affiliates
Symetra common shares	360.9		288.4
Investments in unconsolidated affiliates	317.3	[1],[2]	351.2	[3]	261.0	[3]	350.4
Symetra | Warrants
Investments in unconsolidated affiliates
Investments in unconsolidated affiliates	0	[1],[2]	30.3	[3]	12.6	[3]	37.1
Hamer, LLC
Investments in unconsolidated affiliates
Investments in unconsolidated affiliates	4.1	[4]	4.0	[4]
Bri-Mar Manufacturing, LLC
Investments in unconsolidated affiliates
Investments in unconsolidated affiliates	0	[4]	1.9	[4]
Pentelia Capital Management
Investments in unconsolidated affiliates
Investments in unconsolidated affiliates	$ 0		$ 0.5

[1] Equity in earnings for the years end December 31, 2013, 2012 and 2011 excludes tax expense of $2.8, $2.6, and $2.3

[2] The aggregate value of White Mountains’ investment in common shares of Symetra was $380.1 based upon the quoted market price of $18.96 per share at December 31, 2013.

[3] Includes White Mountains’ equity in net unrealized (losses) gains from Symetra’s fixed maturity portfolio of $(43.6), $62.8, and $0 as of December 31, 2013, 2012 and 2011, which excludes tax benefit (expense) of $3.2, $(5.1) and $0

[4] As of October 1, 2012, Hamer and Bri-Mar are no longer consolidated and are accounted for as investments in unconsolidated affiliates.