Common Shareholders’ Equity and Noncontrolling Interests - Noncontrolling Interests (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Noncontrolling Interest [Line Items]
Noncontrolling Equity	$ 321.1	$ 188.1
HG Global
Noncontrolling Interest [Line Items]
Noncontrolling Equity	0.8	(0.6)
Ark
Noncontrolling Interest [Line Items]
Noncontrolling Equity	336.9	247.9
Subsidiary - Kudu Investment Management, LLC
Noncontrolling Interest [Line Items]
Noncontrolling Equity	113.8	75.1
Other
Noncontrolling Interest [Line Items]
Noncontrolling Equity	9.4	20.4
Total, excluding BAM
Noncontrolling Interest [Line Items]
Noncontrolling Equity	460.9	342.8
Variable Interest Entity, Primary Beneficiary
Noncontrolling Interest [Line Items]
Noncontrolling Equity	$ (139.8)	$ (154.7)
HG Global
Noncontrolling Interest [Line Items]
Noncontrolling Percentage	3.10%	3.10%
Ark
Noncontrolling Interest [Line Items]
Noncontrolling Percentage	28.00%	28.00%
Subsidiary - Kudu Investment Management, LLC
Noncontrolling Interest [Line Items]
Noncontrolling Percentage	10.50%	10.80%
Build America Mutual Assurance Company
Noncontrolling Interest [Line Items]
Noncontrolling Percentage	100.00%	100.00%