Allocation of Plan Assets by Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	$ 3,494.1	$ 3,115.2	$ 4,094.5
Level 1
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	96.1	88.0
Level 2
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	414.1	375.5
Fair Value Inputs Level 1 And Level 2 [Member]
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	510.2	463.5
MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	2,983.9	2,651.7
U.S. Equities
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	1,004.4	830.9
U.S. Equities | MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	1,004.4	830.9
Global Equities
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	771.8	795.9
Global Equities | MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	771.8	795.9
Total Equities
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	$ 1,776.2	$ 1,626.8
Total Equities | Minimum
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Equity funds, target	45.00%	45.00%
Total Equities | Maximum
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Equity funds, target	65.00%	65.00%
Total Equities | MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	$ 1,776.2	$ 1,626.8
U.S. Fixed Income
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	1,048.0	945.4
U.S. Fixed Income | Level 1
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	95.7	82.2
U.S. Fixed Income | Level 2
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	275.4	258.0
U.S. Fixed Income | Fair Value Inputs Level 1 And Level 2 [Member]
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	371.1	340.2
U.S. Fixed Income | MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	676.9	605.2
Non-U.S. Fixed Income
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	569.5	450.8
Non-U.S. Fixed Income | Level 2
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	39.3	31.4
Non-U.S. Fixed Income | Fair Value Inputs Level 1 And Level 2 [Member]
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	39.3	31.4
Non-U.S. Fixed Income | MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	530.2	419.4
Total Fixed Income
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	$ 1,617.5	$ 1,396.2
Total Fixed Income | Minimum
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Equity funds, target	35.00%	35.00%
Total Fixed Income | Maximum
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Equity funds, target	55.00%	55.00%
Total Fixed Income | Level 1
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	$ 95.7	$ 82.2
Total Fixed Income | Level 2
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	314.7	289.4
Total Fixed Income | Fair Value Inputs Level 1 And Level 2 [Member]
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	410.4	371.6
Total Fixed Income | MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	1,207.1	1,024.6
Cash and Other
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	100.4	92.2
Cash and Other | Level 1
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	0.4	5.8
Cash and Other | Level 2
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	99.4	86.1
Cash and Other | Fair Value Inputs Level 1 And Level 2 [Member]
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	99.8	91.9
Cash and Other | MEASURED AT NAV
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Plan assets	$ 0.6	$ 0.3