CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Millions	Total	Total Equity	Total	Common shares and paid-in surplus	Retained earnings	AOCI, after tax	Non-controlling interest
Beginning Balances at Dec. 31, 2022		$ 3,935.0	$ 3,746.9	$ 538.6	$ 3,211.8	$ (3.5)	$ 188.1
Increase (Decrease) in Shareholders' Equity
Net income (loss)	$ 218.2	218.2	222.7		222.7		(4.5)
Other comprehensive income (loss), net of tax		0.9	0.8			0.8	0.1
Total comprehensive income (loss)	223.6	219.1	223.5		222.7	0.8	(4.4)
Dividends declared on common shares		(2.6)	(2.6)		(2.6)
Dividends to noncontrolling interests		(8.3)					(8.3)
Issuances of common shares		2.1	2.1	2.1
Repurchases and retirements of common shares		(32.7)	(32.7)	(5.1)	(27.6)
BAM member surplus contribution, net of tax		46.4					46.4
Amortization of restricted share awards		11.2	11.2	11.2
Recognition of equity-based compensation expense of subsidiaries		1.8	1.3	1.3			0.5
Impact to noncontrolling interests for the deconsolidation of BAM		(9.4)					(9.4)
Net contributions (distributions) and dilution from other noncontrolling interests		1.6	(0.6)	(0.6)			2.2
Ending Balances at Sep. 30, 2023		4,164.2	3,949.1	547.5	3,404.3	(2.7)	215.1
Beginning Balances at Jun. 30, 2023		4,125.9	3,922.2	543.2	3,380.7	(1.7)	203.7
Increase (Decrease) in Shareholders' Equity
Net income (loss)	13.8	13.8	23.6		23.6		(9.8)
Other comprehensive income (loss), net of tax		(1.7)	(1.0)			(1.0)	(0.7)
Total comprehensive income (loss)	21.9	12.1	22.6		23.6	(1.0)	(10.5)
Dividends to noncontrolling interests		(0.5)					(0.5)
BAM member surplus contribution, net of tax		19.9					19.9
Amortization of restricted share awards		4.0	4.0	4.0
Recognition of equity-based compensation expense of subsidiaries		0.6	0.4	0.4			0.2
Net contributions (distributions) and dilution from other noncontrolling interests		2.2	(0.1)	(0.1)			2.3
Ending Balances at Sep. 30, 2023		4,164.2	3,949.1	547.5	3,404.3	(2.7)	215.1
Beginning Balances at Dec. 31, 2023	4,561.6	4,561.6	4,240.5	551.3	3,690.8	(1.6)	321.1
Increase (Decrease) in Shareholders' Equity
Net income (loss)	408.5	408.5	360.8		360.8		47.7
Other comprehensive income (loss), net of tax		1.1	0.6			0.6	0.5
Total comprehensive income (loss)	361.9	409.6	361.4		360.8	0.6	48.2
Dividends declared on common shares		(2.5)	(2.5)		(2.5)
Dividends to noncontrolling interests		(9.3)					(9.3)
Issuances of common shares		2.9	2.9	2.9
Repurchases and retirements of common shares		(8.1)	(8.1)	(1.1)	(7.0)
BAM member surplus contribution, net of tax		26.0					26.0
Amortization of restricted share awards		11.8	11.8	11.8
Recognition of equity-based compensation expense of subsidiaries		3.1	2.3	2.3			0.8
Impact to noncontrolling interests for the deconsolidation of BAM		153.5					153.5
Net contributions (distributions) and dilution from other noncontrolling interests		0.1	2.3	(3.9)	6.2		(2.2)
Acquisition of noncontrolling interests - Bamboo		111.1					111.1
Ending Balances at Sep. 30, 2024	5,259.8	5,259.8	4,610.6	563.3	4,048.3	(1.0)	649.2
Beginning Balances at Jun. 30, 2024		4,872.2	4,422.6	561.3	3,863.1	(1.8)	449.6
Increase (Decrease) in Shareholders' Equity
Net income (loss)	227.9	227.9	179.0		179.0		48.9
Other comprehensive income (loss), net of tax		1.3	0.8			0.8	0.5
Total comprehensive income (loss)	180.3	229.2	179.8		179.0	0.8	49.4
Amortization of restricted share awards		4.3	4.3	4.3
Recognition of equity-based compensation expense of subsidiaries		1.0	0.8	0.8			0.2
Impact to noncontrolling interests for the deconsolidation of BAM		153.5					153.5
Net contributions (distributions) and dilution from other noncontrolling interests		(0.4)	3.1	(3.1)	6.2		(3.5)
Ending Balances at Sep. 30, 2024	$ 5,259.8	$ 5,259.8	$ 4,610.6	$ 563.3	$ 4,048.3	$ (1.0)	$ 649.2