CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Millions	Total	Common shares and paid-in surplus	Retained earnings	AOCI, after-tax	Parent	Non-controlling Interests	Total Equity includes Noncontrolling Interest [Member]	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) Parent	Foreign Currency Gain (Loss) Non-controlling Interests	Foreign Currency Gain (Loss) Total Equity includes Noncontrolling Interest [Member]	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 Parent	Pension liability and other accumulated comprehensive items Non-controlling Interests	Pension liability and other accumulated comprehensive items Total Equity includes Noncontrolling Interest [Member]	Prospector Turtle Fund Common shares and paid-in surplus	Prospector Turtle Fund Retained earnings	Prospector Turtle Fund AOCI, after-tax	Prospector Turtle Fund Parent	Prospector Turtle Fund Non-controlling Interests	Prospector Turtle Fund Total Equity includes Noncontrolling Interest [Member]
Beginning balance at Dec. 31, 2012		$ 1,057.2	$ 2,542.5	$ 131.9	$ 3,731.6	$ 526.3	$ 4,257.9
Increase (Decrease) in Shareholders' Equity
Net income	$ 309.1	0.0	321.6	0.0	321.6	(12.5)	309.1
Net change in unrealized (losses) gains on investments in unconsolidated affiliates, after tax	(98.1)	0.0	0.0	(98.1)	(98.1)	0.0	(98.1)
Other comprehensive income (loss), after-tax														$ 0.0	$ 0.0	$ 15.6	$ 15.6	$ 5.2	$ 20.8
Change in foreign currency translation, net of tax	2.7							$ 0.0	$ 0.0	$ 2.7	$ 2.7	$ 0.0	$ 2.7
Net change in pension liability and other accumulated comprehensive items	20.8
Comprehensive income	247.0	0.0	321.6	(79.8)	241.8	(7.3)	234.5
Dividends declared on common shares		0.0	(6.2)	0.0	(6.2)	0.0	(6.2)
Dividends/distributions to non-controlling interests		0.0	0.0	0.0	0.0	(39.7)	(39.7)
Issuances of common shares		1.0	0.0	0.0	1.0	0.0	1.0
Repurchases and retirements of common shares	(79.8)	(23.8)	(56.0)	0.0	(79.8)	0.0	(79.8)
Noncontrolling Interest, Increase from Subsidiary Equity Issuance		0.0	0.0	0.0	0.0	11.5	11.5
Amortization of restricted share and option awards		16.7	0.0	0.0	16.7	0.9	17.6
Ending balance at Dec. 31, 2013		1,051.1	2,801.9	52.1	3,905.1	491.7	4,396.8
Increase (Decrease) in Shareholders' Equity
Net income	290.0	0.0	312.2	0.0	312.2	(22.2)	290.0
Net change in unrealized (losses) gains on investments in unconsolidated affiliates, after tax	75.3	0.0	0.0	75.3	75.3	0.0	75.3
Other comprehensive income (loss), after-tax														0.0	0.0	(8.7)	(8.7)	(3.0)	(11.7)
Change in foreign currency translation, net of tax	(168.5)							0.0	0.0	(168.2)	(168.2)	(0.3)	(168.5)
Net change in pension liability and other accumulated comprehensive items	(11.7)
Comprehensive income	207.3	0.0	312.2	(101.6)	210.6	(25.5)	185.1
Dividends declared on common shares		0.0	(6.2)	0.0	(6.2)	0.0	(6.2)
Dividends/distributions to non-controlling interests		0.0	0.0	0.0	0.0	(40.7)	(40.7)
Issuances of common shares		4.8	0.0	0.0	4.8	0.0	4.8
Repurchases and retirements of common shares	(134.5)	(37.1)	(97.4)	0.0	(134.5)	0.0	(134.5)
Noncontrolling Interest, Increase from Subsidiary Equity Issuance		0.0	0.0	0.0	0.0	8.3	8.3
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests		0.0	0.0	0.0	0.0	(122.1)	(122.1)													$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 14.0	$ 14.0
Amortization of restricted share and option awards		15.9	0.0	0.0	15.9	0.8	16.7
Ending balance at Dec. 31, 2014	3,995.7	1,034.7	3,010.5	(49.5)	3,995.7	542.7	4,538.4
Increase (Decrease) in Shareholders' Equity
Net income	279.5	0.0	297.6	0.0	297.6	(18.1)	279.5
Net change in unrealized (losses) gains on investments in unconsolidated affiliates, after tax	(34.9)	0.0	0.0	(34.9)	(34.9)	0.0	(34.9)
Other comprehensive income (loss), after-tax														$ 0.0	$ 0.0	$ 0.3	$ 0.3	$ 0.0	$ 0.3
Change in foreign currency translation, net of tax	(65.8)							$ 0.0	$ 0.0	$ (65.8)	$ (65.8)	$ 0.0	$ (65.8)
Net change in pension liability and other accumulated comprehensive items	0.3
Comprehensive income	197.2	0.0	297.6	(100.4)	197.2	(18.1)	179.1
Dividends declared on common shares		0.0	(6.0)	0.0	(6.0)	0.0	(6.0)
Dividends/distributions to non-controlling interests		0.0	0.0	0.0	0.0	(51.1)	(51.1)
Issuances of common shares		0.9	0.0	0.0	0.9	0.0	0.9
Repurchases and retirements of common shares	(284.2)	(67.0)	(217.2)	0.0	(284.2)	0.0	(284.2)
Noncontrolling Interest, Increase from Subsidiary Equity Issuance		0.0	0.0	0.0	0.0	17.5	17.5
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests		(5.3)	0.0	0.0	(5.3)	(2.7)	(8.0)													$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ (31.5)	$ (31.5)
Amortization of restricted share and option awards		14.9	0.0	0.0	14.9	(2.0)	12.9
Ending balance at Dec. 31, 2015	$ 3,913.2	$ 978.2	$ 3,084.9	$ (149.9)	$ 3,913.2	$ 454.8	$ 4,368.0