Employee Benefits - Narrative (Detail)	1 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Aug. 31, 2020 USD ($)	Jun. 30, 2021	Sep. 30, 2021	Dec. 31, 2021 USD ($) investment numberOfDerivativeInstruments age	Dec. 31, 2020 USD ($) numberOfDerivativeInstruments	Dec. 31, 2019 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Actuarial Loss (Gain)				$ (31,500,000)	$ 176,000,000
Number of investments held in diversified portfolios | investment				1
Number of derivatives held by the plan | numberOfDerivativeInstruments				3	5
Expected long-term rate of return on assets				5.25%
Postretirement Health Care, minimum retirement age | age				55
Postretirement Health Care, minimum service term				15 years
Estimated contribution defined contribution plans				$ 65,300,000	$ 62,900,000	$ 57,600,000
Trust for Benefit of Employees
Defined Benefit Plan Disclosure [Line Items]
Assets related to the pension plan				$ 117,800,000	137,500,000
Long Credit Bonds
Defined Benefit Plan Disclosure [Line Items]
Target allocation of plan assets				55.00%
Global Equities
Defined Benefit Plan Disclosure [Line Items]
Target allocation of plan assets				15.00%
Custom Completion
Defined Benefit Plan Disclosure [Line Items]
Target allocation of plan assets				10.00%
High Yield Bonds
Defined Benefit Plan Disclosure [Line Items]
Target allocation of plan assets				4.00%
Northern Trust Private Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Target allocation of plan assets				5.00%
Northern Trust Private Equity Funds | Upper Limit
Defined Benefit Plan Disclosure [Line Items]
Target allocation of plan assets				20.00%
Emerging Market Debt
Defined Benefit Plan Disclosure [Line Items]
Target allocation of plan assets				3.00%
Global Listed Infrastructure
Defined Benefit Plan Disclosure [Line Items]
Target allocation of plan assets				3.00%
Real Estate
Defined Benefit Plan Disclosure [Line Items]
Target allocation of plan assets				3.00%
Northern Trust Hedge Fund
Defined Benefit Plan Disclosure [Line Items]
Target allocation of plan assets				2.00%
Supplemental Plan
Defined Benefit Plan Disclosure [Line Items]
Assets related to the pension plan				$ 0	0
Prior service costs, amortization period (years)				10 years
Actuarial Loss (Gain)				$ (2,000,000.0)	20,400,000
Prior service (benefit) cost				$ 100,000	$ 200,000	200,000
Weighted average discount rate used in determining the accumulated postretirement benefit obligation				2.80%	2.45%
Other Postretirement Plan
Defined Benefit Plan Disclosure [Line Items]
Prior service costs, amortization period (years)	13 years 10 months 24 days
Actuarial Loss (Gain)				$ (3,300,000)	$ (100,000)
Prior service (benefit) cost	$ (12,700,000)			$ (900,000)	$ (300,000)	0
Weighted average discount rate used in determining the accumulated postretirement benefit obligation				2.56%	2.16%
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Assets related to the pension plan				$ 1,708,900,000	$ 1,793,700,000
Contributions made to the pension plan				$ 6,700,000	10,600,000
Pension Plans, Defined Benefit | Lower Limit
Defined Benefit Plan Disclosure [Line Items]
Fair value, investments, entities that calculate net asset value per share, liquidating investment, remaining period				1 year
Pension Plans, Defined Benefit | Upper Limit
Defined Benefit Plan Disclosure [Line Items]
Fair value, investments, entities that calculate net asset value per share, liquidating investment, remaining period				15 years
Pension Plans, Defined Benefit | Northern Trust Private Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Assets related to the pension plan				$ 34,500,000	20,300,000
Pension Plans, Defined Benefit | Northern Trust Hedge Fund
Defined Benefit Plan Disclosure [Line Items]
Assets related to the pension plan				$ 36,700,000	34,200,000
Fair value, investments, entities that calculate net asset value per share, investment redemption, notice period				60 days
Pension Plans, Defined Benefit | Domestic Common Stock
Defined Benefit Plan Disclosure [Line Items]
Assets related to the pension plan				$ 17,500,000	13,500,000
Pension Plans, Defined Benefit | Real Estate Funds
Defined Benefit Plan Disclosure [Line Items]
Assets related to the pension plan				$ 79,300,000	46,100,000
Fair value, investments, entities that calculate net asset value per share, investment redemption, notice period				45 days
U.S. Plan | Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Assets related to the pension plan				$ 1,708,900,000	1,793,700,000	$ 1,601,200,000
Contributions made to the pension plan				$ 0	0
Prior service costs, amortization period (years)				11 years
Actuarial Loss (Gain)				$ (19,100,000)	$ 136,500,000
Expected long-term rate of return on assets					5.25%	6.00%
Prior service (benefit) cost				$ (400,000)	$ (400,000)	$ (400,000)
Weighted average discount rate used in determining the accumulated postretirement benefit obligation		3.05%	3.06%	3.03%	2.75%
U.S. Plan | Pension Plans, Defined Benefit | Lower Limit
Defined Benefit Plan Disclosure [Line Items]
Contribution to plan assets				$ 0
Expected long-term rate of return on assets		5.25%	5.00%	5.25%	5.25%
U.S. Plan | Pension Plans, Defined Benefit | Upper Limit
Defined Benefit Plan Disclosure [Line Items]
Contribution to plan assets				$ 413,000,000
Expected long-term rate of return on assets				5.00%