Fair Values of Financial Instruments Private Equity Partnerships (Details) - Private Equity Funds - USD ($) $ in Millions		Dec. 31, 2025	Dec. 31, 2024
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share
Alternative Investments		$ 1,456.3	$ 1,450.6
Alternative Investments, Unfunded Commitments		756.7	768.5
Private Credit
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share
Alternative Investments		255.8	289.2
Alternative Investments, Unfunded Commitments		121.0	129.2
Private Credit | Not Redeemable
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share
Alternative Investments	[1]	205.9	236.9
Alternative Investments, Unfunded Commitments	[1]	108.3	118.9
Private Credit | Quarterly/ 90 days notice [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share
Alternative Investments		49.9	52.3
Alternative Investments, Unfunded Commitments		12.7	10.3
Private Equity Limited Partnership
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share
Alternative Investments		651.4	640.2
Alternative Investments, Unfunded Commitments		422.3	409.2
Private Equity Limited Partnership | Not Redeemable
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share
Alternative Investments	[2]	618.9	604.1
Alternative Investments, Unfunded Commitments	[2]	406.8	398.2
Private Equity Limited Partnership | Quarterly after 5.5 year lock with 90 days notice [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share
Alternative Investments		32.5	36.1
Alternative Investments, Unfunded Commitments		15.5	11.0
Real Assets
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share
Alternative Investments		549.1	521.2
Alternative Investments, Unfunded Commitments		213.4	230.1
Real Assets | Not Redeemable
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share
Alternative Investments	[3]	511.4	486.6
Alternative Investments, Unfunded Commitments	[3]	213.4	230.1
Real Assets | Quarterly/ 90 days notice [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share
Alternative Investments		37.7	34.6
Alternative Investments, Unfunded Commitments		$ 0.0	$ 0.0

[1] Private Credit - The limited partnerships described in this category employ various investment strategies, generally providing direct lending or other forms of debt financing including first-lien, second-lien, mezzanine, and subordinated loans. The limited partnerships have credit exposure to corporates, physical assets, and/or financial assets within a variety of industries (including manufacturing, healthcare, energy, business services, technology, materials, and retail) in North America and, to a lesser extent, outside of North America.  As of December 31, 2025, the estimated remaining life of the investments that do not allow for redemptions is approximately 79 percent in the next 3 years, 6 percent during the period from 3 to 5 years, and 15 percent during the period from 5 to 10 years.

[2] Private Equity - The limited partnerships described in this category employ various strategies generally investing in controlling or minority control equity positions directly in companies and/or assets across various industries (including manufacturing, healthcare, energy, business services, technology, materials, and retail), primarily in private markets within North America and, to a lesser extent, outside of North America.  As of December 31, 2025, the estimated remaining life of the investments that do not allow for redemptions is approximately 45 percent in the next 3 years, 21 percent during the period from 3 to 5 years, 33 percent during the period from 5 to 10 years, and 1 percent during the period from 10 to 15 years.

[3] Real Assets - The limited partnerships described in this category employ various strategies, which include investing in the equity and/or debt financing of physical assets, including infrastructure (energy, power, water/wastewater, communications), transportation (including airports, ports, toll roads, aircraft, railcars) and real estate in North America, Europe, South America, and Asia.  As of December 31, 2025, the estimated remaining life of the investments that do not allow for redemptions is approximately 47 percent in the next 3 years, 30 percent during the period from 3 to 5 years, and 23 percent during the period from 5 to 10 years.