CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 OneBeacon	Dec. 31, 2011 OneBeacon	Dec. 31, 2010 OneBeacon
Cash flows from operations:
Net income	$ 193.4	$ 809.4	$ 139.5
Charges (credits) to reconcile net income to net cash (used for) provided from operations:
Net realized and unrealized investment gains	(118.2)	(74.1)	(77.6)
Excess of fair value of acquired net assets over cost and gain on sale of subsidiaries	(34.2)	(7.2)	(12.8)
Deferred income tax (benefit) expense	(16.8)	(71.0)	70.7
Undistributed equity in (earnings) loss from unconsolidated affiliates, after-tax	(29.9)	20.2	(9.9)
Net loss from other discontinued operations	24.0	36.7	30.1
Gain (loss) on sale of discontinued operation, net of tax				91.0	19.2	0
Other operating items:
Net change in loss and loss adjustment expense reserves	(172.2)	(23.4)	(73.6)
Net change in reinsurance recoverable on paid and unpaid losses	42.4	66.0	115.2
Net change in unearned insurance and reinsurance premiums	63.1	67.0	(24.7)
Net change in ceded reinsurance premiums payable	3.8	39.5	0.5
Net change in ceded unearned insurance and reinsurance premiums	0	(8.6)	4.4
Net change in insurance and reinsurance premiums receivable	(79.2)	(42.4)	(123.4)
Net change in variable annuity benefit guarantee liabilities	(327.1)	158.3	229.5
Net change in variable annuity benefit derivative instruments	192.1	57.1	(153.0)
Net change in deferred acquisition costs	(5.7)	(15.3)	(2.3)
Net change in funds held by ceding companies	(17.7)	11.6	16.4
Net change in funds held under reinsurance treaties	10.6	(42.4)	(10.6)
Net change in other assets and liabilities, net	151.0	(229.0)	(89.5)
Net cash (used for) provided from continuing operations	(29.6)	94.1	28.9
Net cash (used for) provided from discontinuing operations	(196.2)	(208.6)	27.1
Net cash (used for) provided from operations	(225.8)	(114.5)	56.0
Cash flows from investing activities:
Net change in short-term investments	145.3	174.5	475.6
Sales of fixed maturity and convertible fixed maturity investments	6,040.0	3,481.9	2,447.8
Maturities, calls and paydowns of fixed maturities and convertible fixed maturities	678.4	1,163.6	1,744.1
Sales of common equity securities	192.4	237.8	167.5
Distributions and redemptions of other long-term investments	86.7	150.7	133.2
Sales of unconsolidated affiliates, net of cash sold and held in escrow	24.8	1,010.6	188.3
Contributions to other long-term investments	(96.7)	(65.8)	(111.1)
Contributions to discontinued operations	(196.2)	(171.8)	(48.1)
Purchases of common equity securities	(365.2)	(297.8)	(273.6)
Purchases of fixed maturity and convertible fixed maturity investments	(5,810.1)	(5,200.6)	(4,217.7)
Purchases of consolidated and unconsolidated affiliates, net of cash acquired	(41.3)	(3.2)	(4.9)
Net change in unsettled investment purchases and sales	(22.4)	47.0	1.6
Net acquisitions of property and equipment	(2.3)	(5.5)	(5.8)
Net cash provided from investing activities — continuing operations	633.4	521.4	496.9
Net cash provided from (used for) investing activities — discontinued operations	196.2	278.2	(11.6)
Net cash provided from investing activities	829.6	799.6	485.3
Cash flows from financing activities:
Repayment of debt	(75.0)	0	(14.0)
Repurchase of debt	(275.9)	(161.6)	(197.3)
Issuance of debt, net of debt issuance costs	271.9	0	0
Draw down of revolving line of credit	150.0	0	0
Repayments of Long-term Capital Lease Obligations	(4.9)
Capital lease obligation		23.1	0
Cash dividends paid to the Company’s common shareholders	(6.6)	(8.0)	(8.8)
Cash dividends paid to OneBeacon Ltd.’s non-controlling common shareholders	(19.8)	(42.8)	(75.9)
Cash dividends paid on SIG Preference Shares	(18.8)	(18.8)	(18.8)
Common shares repurchased	(669.1)	(253.0)	(225.6)
OneBeacon Ltd. common shares repurchased and retired	0	0	(10.5)
Proceeds from issuances of common shares	0	0.9	0.7
Net cash used for financing activities — continuing operations	(648.2)	(460.2)	(550.2)
Net cash provided from financing activities — discontinued operations	0	0	0
Net cash used for financing activities	(648.2)	(460.2)	(550.2)
Effect of exchange rate changes on cash	3.1	(1.5)	8.1
Net change in cash during the period	(41.3)	223.4	(0.8)
Net change in cash from discontinued operations	0	(69.6)	(15.5)
Cash reclassified to assets held for sale (net of cash sold of $3.5, $0, and $0)	2.0	(5.5)	0
Cash balance at beginning of year (excludes restricted cash balances of $453.5, $286.7 and $217.1 and AutoOne cash of $0, $4.7 and $3.9)	251.9	103.6	119.9
Cash balance at end of year (excludes restricted cash balances of $249.8, $453.5, and $286.7 and AutoOne cash of $0, $0, and $4.7)	$ 212.6	$ 251.9	$ 103.6