Pensions and Other Post-retirement Benefits - Schedule of Expected Return on Assets for Net Periodic Pension Cost (Detail)	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Pension Plan Assets at December 31,	100.00%	100.00%
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Pension Plan Assets at December 31,	49.00%	46.00%
Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Pension Plan Assets at December 31,	25.00%	30.00%
Pooled investment funds
Defined Benefit Plan Disclosure [Line Items]
Pension Plan Assets at December 31,	21.00%	19.00%
Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Pension Plan Assets at December 31,	4.00%	4.00%
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension Plan Assets at December 31,	1.00%	1.00%