CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Millions	Total	Common shares and paid-in surplus	Retained earnings	AOCI, after tax	Total	Non-controlling interest	Total Equity	Foreign Currency Gain (Loss) Common shares and paid-in surplus	Foreign Currency Gain (Loss) Retained earnings	Foreign Currency Gain (Loss) AOCI, after tax	Foreign Currency Gain (Loss) Total	Foreign Currency Gain (Loss) Non-controlling interest	Foreign Currency Gain (Loss) Total Equity	Pension liability and other accumulated comprehensive items Common shares and paid-in surplus	Pension liability and other accumulated comprehensive items Retained earnings	Pension liability and other accumulated comprehensive items AOCI, after tax	Pension liability and other accumulated comprehensive items Total	Pension liability and other accumulated comprehensive items Non-controlling interest	Pension liability and other accumulated comprehensive items Total Equity	Prospector Turtle Fund Common shares and paid-in surplus	Prospector Turtle Fund Retained earnings	Prospector Turtle Fund AOCI, after tax	Prospector Turtle Fund Total	Prospector Turtle Fund Non-controlling interest	Prospector Turtle Fund Total Equity	Sale of Sirius Group [Member] Common shares and paid-in surplus	Sale of Sirius Group [Member] Retained earnings	Sale of Sirius Group [Member] AOCI, after tax	Sale of Sirius Group [Member] Total	Sale of Sirius Group [Member] Non-controlling interest	Sale of Sirius Group [Member] Total Equity	Sale of Sirius Group [Member] Foreign Currency Gain (Loss) Common shares and paid-in surplus	Sale of Sirius Group [Member] Foreign Currency Gain (Loss) Retained earnings	Sale of Sirius Group [Member] Foreign Currency Gain (Loss) AOCI, after tax	Sale of Sirius Group [Member] Foreign Currency Gain (Loss) Total	Sale of Sirius Group [Member] Foreign Currency Gain (Loss) Non-controlling interest	Sale of Sirius Group [Member] Foreign Currency Gain (Loss) Total Equity
Balances at Dec. 31, 2014		$ 1,034.7	$ 3,010.5	$ (49.5)	$ 3,995.7	$ 542.7	$ 4,538.4
Increase (Decrease) in Shareholders' Equity
Net income	$ 80.4	0.0	88.6	0.0	88.6	(8.2)	80.4
Net change in unrealized gains (losses) from investments in unconsolidated affiliates	(32.9)	0.0	0.0	(32.9)	(32.9)	0.0	(32.9)
Net change in foreign currency translation	0.2							$ 0.0	$ 0.0	$ (43.8)	$ (43.8)	$ (0.1)	$ (43.9)
Net change in pension liability and other accumulated comprehensive items														$ 0.0	$ 0.0	$ 0.4	$ 0.4	$ 0.1	$ 0.5
Total comprehensive income (loss)	12.3	0.0	88.6	(76.3)	12.3	(8.2)	4.1
Dividends declared on common shares		0.0	(6.0)	0.0	(6.0)	0.0	(6.0)
Dividends to non-controlling interests	1.0	0.0	0.0	0.0	0.0	(21.9)	(21.9)
Repurchases and retirements of common shares		(8.8)	(23.9)	0.0	(32.7)	0.0	(32.7)
Issuances of common shares		0.9	0.0	0.0	0.9	0.0	0.9
Acquisition from non-controlling interests		(2.2)	0.0	0.0	(2.2)	(2.7)	(4.9)													$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ (31.5)	$ (31.5)
Net contributions from non-controlling interests		0.0	0.0	0.0	0.0	5.8	5.8
Amortization of restricted share awards		6.6	0.0	0.0	6.6	(0.3)	6.3
Balances at Jun. 30, 2015		1,031.2	3,069.2	(125.8)	3,974.6	483.9	4,458.5
Balances at Dec. 31, 2015	4,368.0	978.2	3,084.9	(149.9)	3,913.2	454.8	4,368.0
Increase (Decrease) in Shareholders' Equity
Net income	381.8	0.0	354.1	0.0	354.1	27.7	381.8
Net change in unrealized gains (losses) from investments in unconsolidated affiliates	0.0
Net change in foreign currency translation	0.1							$ 0.0	$ 0.0	$ 32.0	$ 32.0	$ 0.0	$ 32.0																			$ 0.0	$ 0.0	$ 113.3	$ 113.3	$ 0.0	$ 113.3
Net change in pension liability and other accumulated comprehensive items														$ 0.0	$ 0.0	$ 0.1	$ 0.1	$ 0.0	$ 0.1
Total comprehensive income (loss)	499.5	0.0	354.1	145.4	499.5	27.7	527.2
Dividends declared on common shares		0.0	(5.4)	0.0	(5.4)	0.0	(5.4)
Dividends to non-controlling interests	0.7	0.0	0.0	0.0	0.0	(12.1)	(12.1)
Repurchases and retirements of common shares		(120.4)	(427.0)	0.0	(547.4)	0.0	(547.4)
Issuances of common shares		9.1	0.0	0.0	9.1	0.0	9.1
Noncontrolling Interest, Decrease from Deconsolidation																										$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 250.0	$ 250.0
Acquisition from non-controlling interests		(2.7)	0.0	0.0	(2.7)	(8.8)	(11.5)
Issuance of shares to non-controlling interests		0.0	0.0	0.0	0.0	0.3	0.3
Net contributions from non-controlling interests		0.0	0.0	0.0	0.0	11.9	11.9
Amortization of restricted share awards		8.9	0.0	0.0	8.9	0.4	9.3
Balances at Jun. 30, 2016	$ 4,099.4	$ 873.1	$ 3,006.6	$ (4.5)	$ 3,875.2	$ 224.2	$ 4,099.4