CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Millions	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010
Cash flows from operations:
Net Income (loss)	$ 15.7	$ (25.0)
Charges (credits) to reconcile net loss to net cash used for operations:
Net realized and unrealized investment gains	(76.6)	(93.1)
Net income (loss) from discontinued operations, net of tax	(2.9)	0.8
Other operating items:
Net change in loss and loss adjustment expense reserves	(158.3)	143.0
Net change in reinsurance recoverable on paid and unpaid losses	182.2	(22.4)
Net change in unearned insurance and reinsurance premiums	74.5	139.2
Net change in funds held by ceding companies	(7.6)	(3.8)
Net change in deferred acquisition costs	(14.7)	26.2
Net change in ceded unearned premiums	48.0	(175.3)
Net change in funds held under reinsurance treaties	(47.7)	(14.7)
Net change in insurance and reinsurance premiums receivable	(124.2)	(178.8)
Net change in ceded reinsurance payable	(65.3)	192.8
Net change in other assets and liabilities, net	31.8	52.0
Net cash (used for) provided from operations - continuing operations	(145.1)	40.9
Net cash provided from operations - discontinued operations	9.5	13.7
Net cash (used for) provided from operations	(135.6)	54.6
Cash flows from investing activities:
Net change in short-term investments	162.7	(181.9)
Sales of fixed maturity and convertible fixed maturity investments	2,110.9	988.0
Maturities, calls and paydowns of fixed maturity and convertible fixed maturity investments	825.7	1,138.0
Sales of common equity securities	84.9	95.9
Distributions and redemptions of other long-term investments	77.9	7.6
Purchases of other long-term investments	(22.7)	(44.4)
Contribution to discontinued operations	(58.7)	(17.2)
Purchases of common equity securities	(91.4)	(188.8)
Purchases of fixed maturity and convertible fixed maturity investments	(2,647.2)	(1,437.1)
Purchases of consolidated and unconsolidated affiliates, net of cash acquired		(4.9)
Net change in unsettled investment purchases and sales	38.5	(23.0)
Net acquisitions of property and equipment	(4.1)	(1.0)
Net cash provided from investing activities - continuing operations	476.5	331.2
Net cash provided from (used for) investing activities - discontinued operations	7.9	(7.4)
Net cash provided from investing activities	484.4	323.8
Cash flows from financing activities:
Repayment of debt		(14.0)
Repurchase of debt	(161.6)	(197.3)
Cash dividends paid to the Company's common shareholders	(8.0)	(8.8)
Cash dividends paid to OneBeacon Ltd.'s noncontrolling common shareholders	(33.0)	(9.8)
Cash dividends paid on White Mountains Re Group, Ltd. Preference Shares	(9.4)	(9.4)
Common shares repurchased	(93.3)	(118.3)
OneBeacon Ltd. common shares repurchased and retired		(5.9)
Proceeds from issuances of common shares	1.0	0.8
Net cash used for financing activities - continuing operations	(304.3)	(362.7)
Net cash provided from (used for) financing activities - discontinued operations	0
Net cash used for financing activities	(304.3)	(362.7)
Effect of exchange rate changes on cash	2.4	(2.2)
Net increase in cash during the period	46.9	13.5
Net decrease in cash from discontinued operations	(17.4)	(6.3)
Cash reclassified to assets held for Personal Lines Transaction		(9.1)
Cash balances at beginning of period (excludes restricted cash balances of $286.7 and $217.1)	108.3	123.9
Cash balances at end of period (excludes restricted cash balances of $345.9 and $195.4)	137.8	122.0
Supplemental cash flows information:
Interest paid	(23.7)	(30.9)
Net income tax payments to national governments	$ (25.3)	$ (8.5)