Investment Securities - Significant Unobservable Inputs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Quantitative information for Level 3 Fair Value Measurements Assets
Other long-term investments	$ 2,958.5	$ 2,150.2
Recent transaction | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Other long-term investments	250.4	23.4
Discounted cash flow | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Other long-term investments	$ 16.5	$ 14.5
Discounted cash flow | Discount Rate | Minimum | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	11.00%	11.00%
Discounted cash flow | Discount Rate | Maximum | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	12.00%	12.00%
Kudu’s Participation Contracts
Quantitative information for Level 3 Fair Value Measurements Assets
New and existing contracts deployed	$ 201.7	$ 103.5
Kudu’s Participation Contracts | Discounted cash flow | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value	$ 1,285.0	$ 1,008.4
Kudu’s Participation Contracts | Discounted cash flow | Discount Rate | Minimum | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	16.00%	17.00%
Kudu’s Participation Contracts | Discounted cash flow | Discount Rate | Maximum | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	25.00%	25.00%
Kudu’s Participation Contracts | Discounted cash flow | Terminal Cash Flow Exit Multiple | Minimum | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	700.00%	700.00%
Kudu’s Participation Contracts | Discounted cash flow | Terminal Cash Flow Exit Multiple | Maximum | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	2200.00%	2200.00%
Kudu’s Participation Contracts | Discounted cash flow | Measurement Input, Pre-Tax Discount Rate | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	19.00%	19.00%
Kudu’s Participation Contracts | Discounted cash flow | Measurement, Input, Pre-Tax Terminal Cash Flow Exit Multiple | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	1400.00%	1400.00%
PassportCard/DavidShield | Discounted cash flow | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value	$ 170.0	$ 150.0
PassportCard/DavidShield | Discounted cash flow | Discount Rate | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	24.00%	24.00%
PassportCard/DavidShield | Discounted cash flow | Terminal Revenue Growth Rate | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	4.00%	4.00%
Elementum | Discounted cash flow | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value	$ 35.0	$ 35.0
Elementum | Discounted cash flow | Discount Rate | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	22.00%	22.00%
Elementum | Discounted cash flow | Terminal Revenue Growth Rate | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	3.00%	4.00%
Preferred securities | Discounted cash flow | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value	$ 35.6	$ 31.4
Preferred securities | Discounted cash flow | Discount Rate | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	8.00%	9.00%
Private equity securities | Discounted cash flow | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value	$ 21.9
Private equity securities | Discounted cash flow | Discount Rate | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	35.00%
Private equity securities | Discounted cash flow | Terminal Revenue Growth Rate | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Discount Rate	4.00%