CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Millions	Total	Total Equity	Common Shares and Paid-in Surplus	Retained Earnings	AOCL, After-tax	Total	Noncontrolling Interests
Beginning balance at Dec. 31, 2021		$ 3,704.7	$ 588.9	$ 2,957.5	$ 1.7	$ 3,548.1	$ 156.6
Increase (Decrease) in Shareholders' Equity
Net income (loss)	$ 792.8	712.4		792.8		792.8	(80.4)
Other comprehensive income (loss), net of tax	(3.8)	(3.8)			(2.9)	(2.9)	(0.9)
Other comprehensive income from discontinued operations, net of tax - NSM Group	(5.2)	(5.2)			(5.2)	(5.2)
Net gain (loss) from foreign currency translation from sale of discontinued operations, net of tax - NSM Group	2.9	2.9			2.9	2.9
Total comprehensive income (loss)		706.3		792.8	(5.2)	787.6	(81.3)
Dividends declared on common shares		(3.0)		(3.0)		(3.0)
Dividends to noncontrolling interests		(8.0)					(8.0)
Issuances of common shares		3.0	3.0			3.0
Issuances of shares of noncontrolling interest		74.6					74.6
Repurchases and retirements of common shares	(615.8)	(615.8)	(90.0)	(525.8)		(615.8)
BAM member surplus contributions, net of tax		81.4					81.4
Amortization of restricted share awards		14.0	14.0			14.0
Recognition of equity-based compensation expense of subsidiaries		9.5	8.6			8.6	0.9
Net contributions (distributions) and dilution from other noncontrolling interests		(14.2)	14.1	(9.7)		4.4	(18.6)
Acquisition of noncontrolling interests		(17.5)					(17.5)
Ending balance at Dec. 31, 2022		3,935.0	538.6	3,211.8	(3.5)	3,746.9	188.1
Increase (Decrease) in Shareholders' Equity
Net income (loss)	509.2	580.9		509.2		509.2	71.7
Other comprehensive income (loss), net of tax	2.4	2.4			1.9	1.9	0.5
Other comprehensive income from discontinued operations, net of tax - NSM Group	0.0
Net gain (loss) from foreign currency translation from sale of discontinued operations, net of tax - NSM Group	0.0
Total comprehensive income (loss)		583.3		509.2	1.9	511.1	72.2
Dividends declared on common shares		(2.6)		(2.6)		(2.6)
Dividends to noncontrolling interests		(8.9)					(8.9)
Issuances of common shares		2.1	2.1			2.1
Repurchases and retirements of common shares	(32.7)	(32.7)	(5.1)	(27.6)		(32.7)
BAM member surplus contributions, net of tax		72.8					72.8
Amortization of restricted share awards		15.3	15.3			15.3
Recognition of equity-based compensation expense of subsidiaries		2.4	1.7			1.7	0.7
Net contributions (distributions) and dilution from other noncontrolling interests		4.3	(1.3)			(1.3)	5.6
Acquisition of noncontrolling interests		(9.4)					(9.4)
Ending balance at Dec. 31, 2023	4,561.6	4,561.6	551.3	3,690.8	(1.6)	4,240.5	321.1
Increase (Decrease) in Shareholders' Equity
Net income (loss)	230.4	284.1		230.4		230.4	53.7
Other comprehensive income (loss), net of tax	(0.1)	(0.1)			(0.1)	(0.1)
Other comprehensive income from discontinued operations, net of tax - NSM Group	0.0
Net gain (loss) from foreign currency translation from sale of discontinued operations, net of tax - NSM Group	0.0
Total comprehensive income (loss)		284.0		230.4	(0.1)	230.3	53.7
Dividends declared on common shares		(2.5)		(2.5)		(2.5)
Dividends to noncontrolling interests		(16.2)					(16.2)
Issuances of common shares		2.9	2.9			2.9
Repurchases and retirements of common shares	(7.9)	(7.9)	(1.1)	(6.8)		(7.9)
BAM member surplus contributions, net of tax		26.0					26.0
Amortization of restricted share awards		16.3	16.3			16.3
Recognition of equity-based compensation expense of subsidiaries		4.4	3.2			3.2	1.2
Net contributions (distributions) and dilution from other noncontrolling interests		(2.2)	(6.2)	7.1		0.9	(3.1)
Impact to noncontrolling interests for the deconsolidation of BAM		153.5					153.5
Acquisition of noncontrolling interests		111.1					111.1
Ending balance at Dec. 31, 2024	$ 5,131.0	$ 5,131.0	$ 566.4	$ 3,919.0	$ (1.7)	$ 4,483.7	$ 647.3