Postretirement Benefit Plans - The Weighted Average Assumptions Used to Determine Net Periodic Benefit Costs (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
United States [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Discount rate	4.30%	3.67%	4.17%
Expected long-term return on plan assets	6.75%	6.75%	7.00%
United Kingdom [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Discount rate	2.80%	2.40%	2.60%
Expected long-term return on plan assets	3.82%	3.71%	3.77%