Pensions and Postretirement Benefits Other than Pensions - Projected Benefit Obligation, Accumulated Benefit Obligation and Fair Value of Plan Assets for Pension Plans (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
All Plans, Less Spectrum | United States
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 672,070	$ 606,138
Accumulated benefit obligation	668,875	604,612
Fair value of plan assets	570,958	530,548
All Plans, Less Spectrum | International
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	490,134	446,686
Accumulated benefit obligation	490,134	446,686
Fair value of plan assets	409,260	379,342
Spectrum Plan
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	516,816	500,739
Accumulated benefit obligation	516,816	500,739
Fair value of plan assets	$ 546,692	$ 516,666