CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operations:
Net income	$ 309,400,000	$ 193,400,000	$ 809,400,000
Charges (credits) to reconcile net income to net cash (used for) provided from operations:
Net realized and unrealized investment gains	(161,700,000)	(118,200,000)	(74,100,000)
Net (gain) loss on sale of consolidated and unconsolidated affiliates	(21,300,000)	0	0
Excess of fair value of acquired net assets over cost	(15,200,000)	(34,200,000)	(7,200,000)
Deferred income tax expense (benefit)	39,700,000	(16,800,000)	(71,000,000)
Undistributed equity in (earnings) loss from unconsolidated affiliates, after-tax	(36,600,000)	(29,900,000)	20,200,000
Net loss from discontinued operations	42,100,000	24,000,000	36,700,000
Net (gain) loss on sale of other discontinued operations	(46,600,000)	91,000,000	(658,300,000)
Other operating items:
Net change in loss and loss adjustment expense reserves	(164,600,000)	(172,200,000)	(23,400,000)
Net change in reinsurance recoverable on paid and unpaid losses	25,000,000	42,400,000	66,000,000
Net change in unearned insurance and reinsurance premiums	(12,500,000)	63,100,000	67,000,000
Net change in ceded reinsurance premiums payable	(28,100,000)	3,800,000	39,500,000
Net change in ceded unearned insurance and reinsurance premiums	1,400,000	0	(8,600,000)
Net change in insurance and reinsurance premiums receivable	12,700,000	(79,200,000)	(42,400,000)
Net change in variable annuity benefit guarantee liabilities	(388,700,000)	(327,100,000)	158,300,000
Net change in variable annuity benefit derivative instruments	29,100,000	192,100,000	57,100,000
Net change in deferred acquisition costs	17,100,000	(5,700,000)	(15,300,000)
Net change in funds held by ceding companies	14,400,000	(17,700,000)	11,600,000
Net change in funds held under reinsurance treaties	98,800,000	10,600,000	(42,400,000)
Net change in restricted cash	193,700,000	203,700,000	(166,800,000)
Net change in other assets and liabilities, net	63,200,000	(52,700,000)	(62,200,000)
Net cash (used for) provided from continuing operations	(28,700,000)	(29,600,000)	94,100,000
Net cash used for discontinued operations	(72,300,000)	(196,200,000)	(208,600,000)
Net cash used for operations	(101,000,000)	(225,800,000)	(114,500,000)
Cash flows from investing activities:
Net change in short-term investments	34,800,000	145,300,000	174,500,000
Sales of fixed maturity and convertible fixed maturity investments	3,879,800,000	6,040,000,000	3,481,900,000
Maturities, calls and paydowns of fixed maturity and convertible fixed maturity investments	465,800,000	678,400,000	1,163,600,000
Sales of common equity securities	521,100,000	192,400,000	237,800,000
Distributions and redemptions of other long-term investments	58,100,000	86,700,000	150,700,000
Sales of unconsolidated affiliates, net of cash sold and held in escrow	32,400,000	24,800,000	1,010,600,000
Contributions to other long-term investments	(36,300,000)	(96,700,000)	(65,800,000)
Funding of operational cash flows for discontinued operations	(72,300,000)	(196,200,000)	(171,800,000)
Purchases of common equity securities	(432,200,000)	(365,200,000)	(297,800,000)
Purchases of fixed maturity and convertible fixed maturity investments	(4,132,000,000)	(5,810,100,000)	(5,200,600,000)
Purchases of consolidated and unconsolidated affiliates (net of cash acquired of $28.5, $9.0 and $2.0)	15,900,000	(41,300,000)	(3,200,000)
Net change in unsettled investment purchases and sales	7,500,000	(22,400,000)	47,000,000
Net acquisitions of property and equipment	(13,100,000)	(2,300,000)	(5,500,000)
Net cash provided from investing activities — continuing operations	329,500,000	633,400,000	521,400,000
Net cash provided from investing activities — discontinued operations	72,300,000	196,200,000	278,200,000
Net cash provided from investing activities	401,800,000	829,600,000	799,600,000
Cash flows from financing activities:
Draw down of revolving line of credit	200,000,000	150,000,000	0
Repayment of revolving line of credit	(275,000,000)	(75,000,000)	0
Repurchase of debt	0	(275,900,000)	(161,600,000)
Issuance of debt, net of debt issuance costs	0	271,900,000	0
Change in capital lease obligation	(5,700,000)	(4,900,000)	23,100,000
Cash dividends paid to the Company’s common shareholders	(6,200,000)	(6,600,000)	(8,000,000)
Cash dividends paid to OneBeacon Ltd.’s non-controlling common shareholders	(19,900,000)	(19,800,000)	(42,800,000)
Cash dividends paid on SIG Preference Shares	(18,800,000)	(18,800,000)	(18,800,000)
Common shares repurchased	(79,800,000)	(669,100,000)	(253,000,000)
Proceeds from issuances of common shares	0	0	900,000
Capital contributions from non-controlling interest of consolidated LPs	1,600,000	0	0
Redemptions paid to non-controlling interest of consolidated LPs	(700,000)	0	0
Purchase of interest rate cap	(9,900,000)	0	0
Collateral provided by interest rate cap counterparties	10,800,000	0	0
Capital contributions from BAM members	17,100,000	0	0
Net cash used for financing activities — continuing operations	(186,500,000)	(648,200,000)	(460,200,000)
Net cash (used for) provided from financing activities — discontinued operations	0	0	0
Net cash used for financing activities	(186,500,000)	(648,200,000)	(460,200,000)
Effect of exchange rate changes on cash	(200,000)	3,100,000	(1,500,000)
Net change in cash during the period	114,100,000	(41,300,000)	223,400,000
Cash reclassified to assets held for sale (net of cash sold of $0, $3.5, and $0)	0	2,000,000	(5,500,000)
Cash balance at beginning of year (excludes restricted cash balances of $249.8, $453.5 and $286.7 and AutoOne cash of $0, $0 and $4.7)	212,600,000	251,900,000	103,600,000
Cash balance at end of year (excludes restricted cash balances of $56.1, $249.8, and $453.5)	326,700,000	212,600,000	251,900,000
Discontinued Operations
Charges (credits) to reconcile net income to net cash (used for) provided from operations:
Net realized and unrealized investment gains	0	0	(700,000)
Net loss from discontinued operations	42,100,000	24,000,000	36,700,000
Net (gain) loss on sale of other discontinued operations	(46,600,000)	91,000,000	(658,300,000)
Cash flows from financing activities:
Net change in cash during the period	$ 0	$ 0	$ (69,600,000)