CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operations:
Net income	$ 470.4	$ 5.5
Charges (credits) to reconcile net income to net cash used for operations:
Net realized and unrealized investment (gains) losses	(84.0)	33.9
Deferred income tax expense (benefit)	12.5	(20.2)
Net income from discontinued operations	(7.1)	(59.1)
Net gain on sale of discontinued operations	(414.5)	(18.2)
Net gain on sale of unconsolidated affiliates and consolidated subsidiaries	(0.5)	(16.1)
Amortization and depreciation	34.7	31.8
Undistributed equity in earnings from unconsolidated affiliates, net of tax	0.0	(18.0)
Other operating items:
Net change in loss and loss adjustment expense reserves	(27.8)	83.3
Net change in reinsurance recoverable on paid and unpaid losses	7.6	(63.3)
Net change in unearned insurance premiums	63.0	54.6
Net change in deferred acquisition costs	(2.0)	(3.6)
Net change in funds held by ceding entities	0.0	32.5
Net change in ceded unearned premiums	(5.6)	(23.5)
Net change in funds held under insurance treaties	18.4	19.3
Net change in insurance premiums receivable	(43.3)	(32.0)
Net change in ceded reinsurance payable	(2.8)	12.4
Net change in restricted cash	5.8	6.9
Net change in other assets and liabilities, net	(150.9)	38.4
Net cash (used for) provided from operations - continuing operations	(126.1)	64.6
Net cash (used for) provided from operations	(142.3)	87.3
Cash flows from investing activities:
Net change in short-term investments	(88.7)	26.6
Sales of fixed maturity and convertible investments	2,433.4	865.0
Maturities, calls and paydowns of fixed maturity and convertible investments	530.3	249.5
Sales of common equity securities	961.1	370.6
Distributions and redemptions of other long-term investments	19.8	56.6
Sales of unconsolidated affiliates and consolidated subsidiaries, net of cash sold	2,657.2	24.0
Proceeds from (Payments to) Noncontrolling Interests	(141.6)	0.0
Distribution from (Contributions to) Discontinued Operations for Investing Activities	(396.6)	17.5
Purchases of other long-term investments	(37.3)	(30.5)
Purchases of common equity securities	(249.7)	(329.4)
Purchases of fixed maturity and convertible investments	(4,435.0)	(1,300.2)
Purchases of unconsolidated affiliates and consolidated subsidiaries, net of cash acquired	(13.7)	(2.4)
Net change in unsettled investment purchases and sales	(107.1)	73.8
Net acquisitions of property and equipment	(3.2)	37.0
Net cash provided from investing activities - continuing operations	1,128.9	58.1
Net cash provided from investing activities	1,342.2	60.9
Cash flows from financing activities:
Draw down of debt and revolving line of credit	352.5	98.5
Repayment of debt and revolving line of credit	(401.8)	(84.5)
Proceeds from Issuance of Common Stock	3.7	0.0
Payments on capital lease obligation	(1.4)	(3.5)
Cash dividends paid to the Company’s common shareholders	(5.4)	(6.0)
Cash dividends paid to OneBeacon Ltd.’s non-controlling common shareholders	(14.2)	(14.8)
Common shares repurchased	(861.0)	(168.6)
OneBeacon Ltd. common shares repurchased and retired	(11.5)	(1.7)
Distribution to non-controlling interest shareholders	(1.0)	(9.1)
Contributions to discontinued operations	(3.0)	(4.1)
Acquisition of additional shares from non-controlling interest	0.0	(9.1)
Payments of contingent consideration related to purchases of consolidated subsidiaries	(7.8)	0.0
Capital contributions from BAM members	28.2	20.3
Net cash used for financing activities - continuing operations	(922.7)	(182.6)
Net cash used for financing activities	(922.9)	(163.0)
Effect of Exchange Rate on Cash and Cash Equivalents	0.0	0.0
Net change in cash during the period - continuing operations	80.1	(59.9)
Cash balances at beginning of period	167.2	232.9
Cash held for sale at the beginning of period	1.2	2.1
Cash held for sale at the end of period	3.8	2.1
Cash balances at end of period	244.7	173.0
Supplemental cash flows information:
Interest paid	(7.0)	(6.3)
Net income tax refund from national governments	13.5	8.0
Discontinued Operations [Member]
Charges (credits) to reconcile net income to net cash used for operations:
Net realized and unrealized investment (gains) losses	1.5	(31.4)
Net income from discontinued operations	9.8	(81.3)
Net gain on sale of discontinued operations	(7.1)	(59.1)
Other operating items:
Net cash (used for) provided from operations - discontinued operations	(16.2)	22.7
Cash flows from investing activities:
Net cash provided from investing activities - discontinued operations	213.3	2.8
Cash flows from financing activities:
Net cash (used for) provided from financing activities - discontinued operations	(0.2)	19.6
Cash balances at beginning of period	150.1	116.6
Cash balances at end of period	0.0	157.6
Supplemental cash flows information:
Net income tax refund from national governments	$ 31.8	$ 30.3