Postretirement Benefit Plans - The Weighted Average Assumptions Used to Determine Net Periodic Benefit Costs (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Expected long-term return on plan assets	7.75%
United States [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Discount rate	4.87%	4.17%	5.06%
Expected long-term return on plan assets	7.75%	7.75%	7.75%
United Kingdom [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Discount rate	4.60%	4.30%	4.90%
Expected long-term return on plan assets	5.84%	5.25%	5.46%