Pensions and Other Post-retirement Benefits - Schedule of Expected Return on Assets for Net Periodic Pension Cost (Detail)	Dec. 31, 2017	Dec. 31, 2016
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,	57.00%	70.00%
Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Pension Plan Assets at December 31,	26.00%	20.00%
Pooled investment funds
Defined Benefit Plan Disclosure [Line Items]
Pension Plan Assets at December 31,	12.00%	5.00%
Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Pension Plan Assets at December 31,	3.00%	4.00%
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension Plan Assets at December 31,	2.00%	1.00%