SCHEDULE II CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Assets:
Cash	$ 705.4	$ 395.0
Fixed maturity investments, at fair value	6,221.9	5,786.1
Common equity securities, at fair value	755.0	667.0
Short-term investments, at amortized cost	846.0	975.3
Other assets	681.9	730.0
Total assets	14,064.0	14,534.1
Liabilities
Accounts payable and other liabilities	534.1	557.5
Total liabilities	9,396.1	10,273.3
White Mountains common shareholders equity	4,087.7	3,653.0
Total liabilities and equity	14,064.0	14,534.1
White Mountains Insurance Group Ltd.
Assets:
Cash	0.7	0.3
Fixed maturity investments, at fair value	1,334.5	5.8
Common equity securities, at fair value	1.9	1.8
Short-term investments, at amortized cost	72.3	54.9
Other assets	5.1	4.5
Investments in consolidated and unconsolidated affiliates	2,687.3	3,821.2
Total assets	4,101.8	3,888.5
Liabilities
Payable to subsidiaries	(2.8)	221.7
Accounts payable and other liabilities	16.9	13.8
Total liabilities	14.1	235.5
White Mountains common shareholders equity	4,087.7	3,653.0
Total liabilities and equity	$ 4,101.8	$ 3,888.5