Pension and Postretirement Benefits - Schedule of Plan Assets at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	$ 1,204.2	$ 1,282.7
Total
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	768.9	871.7
Total | Short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	17.0	23.4
Total | Total Aon Collective Investment Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	751.9	848.3
Total | Equity funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	238.1	222.3
Total | Real estate funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	5.8	3.3
Total | Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	508.0	622.7
Quoted prices in active markets for identical assets (Level I)
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	768.9	871.7
Quoted prices in active markets for identical assets (Level I) | Short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	17.0	23.4
Quoted prices in active markets for identical assets (Level I) | Total Aon Collective Investment Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	751.9	848.3
Quoted prices in active markets for identical assets (Level I) | Equity funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	238.1	222.3
Quoted prices in active markets for identical assets (Level I) | Real estate funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	5.8	3.3
Quoted prices in active markets for identical assets (Level I) | Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	508.0	622.7
Significant other observable inputs (Level II)
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0.0	0.0
Significant other observable inputs (Level II) | Short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0.0	0.0
Significant other observable inputs (Level II) | Total Aon Collective Investment Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0.0	0.0
Significant other observable inputs (Level II) | Equity funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0.0	0.0
Significant other observable inputs (Level II) | Real estate funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0.0	0.0
Significant other observable inputs (Level II) | Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0.0	0.0
Significant unobservable inputs (Level III)
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0.0	0.0
Significant unobservable inputs (Level III) | Short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0.0	0.0
Significant unobservable inputs (Level III) | Total Aon Collective Investment Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0.0	0.0
Significant unobservable inputs (Level III) | Equity funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0.0	0.0
Significant unobservable inputs (Level III) | Real estate funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0.0	0.0
Significant unobservable inputs (Level III) | Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0.0	0.0
Other Investments Measured at Net Asset Value | Total Aon Collective Investment Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	40.3	92.4
Other Investments Measured at Net Asset Value | Total other investments measured at net asset value
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	435.3	411.0
Other Investments Measured at Net Asset Value | Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	144.3	76.3
Other Investments Measured at Net Asset Value | Venture Capital Fund
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	6.8	6.6
Other Investments Measured at Net Asset Value | Other Non-U.S. commingled equity and fixed income
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	210.1	$ 235.7
Other Investments Measured at Net Asset Value | NISA Collective Investment Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	$ 33.8