Consolidated Statements of Shareholder's Equity - USD ($) $ in Millions	Common shares	Additional paid-in surplus	Retained earnings	Accumulated other comprehensive (loss)	Total common shareholder's equity	Non-controlling interests	Total
Balance at beginning of period, as adjusted			$ 1,009.0
Accumulated other comprehensive income (loss), other
Non-controlling interests							$ 250.1
Total common shareholder's equity at Dec. 31, 2015	$ 0.1	$ 1,096.1	1,009.0	$ (146.1)
Capital contribution from former parent		89.6
Stock split	1.1	(1.1)
Net income (loss)			51.8
Income attributable to non-controlling interests			(19.3)
Dividends to former parent			27.0
Balance at beginning of year at Dec. 31, 2015				(144.9)
Accumulated net foreign currency translation gains (losses)
Net change in foreign currency translation				(67.3)
Balance at end of year at Dec. 31, 2016				(212.2)
Balance, beginning of period at Dec. 31, 2015				(1.2)			(146.1)
Accumulated other comprehensive income (loss), other
Net change, other				1.2			(66.1)
Balance, end of period at Dec. 31, 2016							$ (212.2)
Total common shareholder's equity at Dec. 31, 2016	1.2	1,184.6	1,014.5	(212.2)	$ 1,988.1
Accumulated other comprehensive income (loss), other
Dividends declared per common share							$ 0.23
Balance at beginning of period, as adjusted			1,014.5
Non-controlling interests						$ 251.3	$ 251.3
Total equity							2,239.4
Capital contribution from former parent		13.3
Net income (loss)			(136.3)
Income attributable to non-controlling interests			(13.7)
Accrued dividends on Series A redeemable preference shares			(6.1)				(6.1)
Net change in foreign currency translation				71.7
Balance at end of year at Dec. 31, 2017				(140.5)
Accumulated other comprehensive income (loss), other
Net change, other							71.7
Balance, end of period at Dec. 31, 2017							(140.5)
Total common shareholder's equity at Dec. 31, 2017	1.2	1,197.9	858.4	(140.5)	1,917.0		1,917.0
Cumulative effect of an accounting change			1.6
Balance at beginning of period, as adjusted			860.0
Accumulated other comprehensive income (loss), other
Non-controlling interests						0.2	0.2
Total equity							1,917.2
Issuance of common shares	0.1	52.7
Share compensation expense		2.5
Share repurchase from CM Bermuda	(0.1)	(163.9)
Return of capital to CM Bermuda		(1.6)
Capital contribution from former parent		1.4
Other, net		0.1
Net income (loss)			(16.7)
Income attributable to non-controlling interests			(1.4)
Accrued dividends on Series A redeemable preference shares			(2.6)				(2.6)
Change in carrying value of Series B preference shares			(36.4)
Redemption of Series A redeemable preference shares			13.8
Other, net			(0.1)
Net change in foreign currency translation				(61.9)
Balance at end of year at Dec. 31, 2018				(202.4)
Accumulated other comprehensive income (loss), other
Net change, other							(61.9)
Balance, end of period at Dec. 31, 2018							(202.4)
Total common shareholder's equity at Dec. 31, 2018	$ 1.2	$ 1,089.1	$ 816.6	$ (202.4)	$ 1,704.5		1,704.5
Accumulated other comprehensive income (loss), other
Non-controlling interests						$ 1.7	1.7
Total equity							$ 1,706.2