Employee Benefit Plans - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2015 USD ($)	Dec. 31, 2015 GBP (£)	Dec. 31, 2015 Rate	Dec. 31, 2014 USD ($) Rate	Dec. 31, 2013 USD ($) Rate	Dec. 31, 2013 GBP (£) Rate	Dec. 31, 2012
Pension and Other Postretirement Benefits Disclosure
Health Care Cost Trend Rate Assumed for Next Fiscal Year | Rate					7.50%
Ultimate Health Care Cost Trend Rate | Rate					5.00%
Effect of One Percentage Point Increase on Service and Interest Cost Components			$ 200,000
Effect of One Percentage Point Decrease on Service and Interest Cost Components			(100,000)
Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation			4,300,000
Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation			(3,200,000)
Future Amortization of Actuarial Gain (Loss)			16,500,000
Future Amortization of Prior Service Cost (Credit)			500,000
Pension Benefits, U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Plan Amendments			7,500,000			$ 0
Pension Plan Lump-sum Settlement Payment			0			214,500,000
Pension Settlement Costs			$ 0			$ 64,400,000	$ 0
Discount Rate Assumptions Used Calculating Benefit Obligation	4.80%	4.80%	4.80%	4.80%	4.80%	4.40%
Expected Long-term Return on Assets Assumptions Used Calculating Net Periodic Benefit Cost		7.50%				7.50%
Decrease in Pension Liability Due to Remeasurement							327,400,000
Tax Impact of Curtailments							114,600,000
Recognized Net Gain (Loss) Due to Curtailments			$ 0			$ 0	(700,000)
Average Remaining Life Expectancy of Plan Participants	25 years
General Discussion of Pension and Other Postretirement Benefits	We had no regulatory contribution requirements for our U.S. qualified defined benefit plan in 2015
Pension Benefits, Non U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Plan Amendments			0			0
Pension Plan Lump-sum Settlement Payment			0			0
Pension Settlement Costs			$ 0			$ 0	0
Discount Rate Assumptions Used Calculating Benefit Obligation	3.80%	3.80%	3.80%	3.80%	3.80%	3.60%
Expected Long-term Return on Assets Assumptions Used Calculating Net Periodic Benefit Cost		5.20%				6.10%
Decrease in Pension Liability Due to Remeasurement							2,300,000	£ 1,500,000
Recognized Net Gain (Loss) Due to Curtailments			$ 0			$ 0	$ 3,700,000	£ 2,300,000
Maximum Inflation Rate on Pensionable Earnings | Rate						2.50%	5.00%	5.00%
Average Remaining Life Expectancy of Plan Participants	34 years
Pension Contributions			0
Other Postretirement Benefit Plans
Pension and Other Postretirement Benefits Disclosure
Plan Amendments			0			$ 0
Pension Plan Lump-sum Settlement Payment			0			0
Pension Settlement Costs			$ 0			$ 0	$ 0
Discount Rate Assumptions Used Calculating Benefit Obligation	4.70%	4.70%	4.70%	4.70%	4.70%	4.30%
Expected Long-term Return on Assets Assumptions Used Calculating Net Periodic Benefit Cost		5.75%			5.75%	5.75%
Recognized Net Gain (Loss) Due to Curtailments			$ 0			$ 0	$ 0
Level 3 Transfers Into			0			0
Level 3 Transfers Out of			0			$ 0
Interest Rate During Period		5.24%				5.46%
Health Care Cost Trend Rate Assumed for Next Fiscal Year | Rate						7.50%
Equity Securites | Pension Benefits, U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Target Plan Asset Allocations | Rate					35.00%
Fixed Maturity Securities | Pension Benefits, U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Target Plan Asset Allocations | Rate					40.00%
Alternative Investments | Pension Benefits, U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Target Plan Asset Allocations | Rate					25.00%
Diversified Growth Assets | Pension Benefits, Non U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Target Plan Asset Allocations | Rate					70.00%
Interest Rate Contract | Pension Benefits, Non U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Target Plan Asset Allocations | Rate					30.00%
Minimum
Pension and Other Postretirement Benefits Disclosure
Private Equity Partnership Future Liquidation Term	1 year
Minimum | Private Equity Funds | Pension Benefits, U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Private Equity Partnership Future Liquidation Term	5 years
Maximum
Pension and Other Postretirement Benefits Disclosure
Private Equity Partnership Future Liquidation Term	12 years
Maximum | Private Equity Funds | Pension Benefits, U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Private Equity Partnership Future Liquidation Term	8 years
Prior to Pension Amendments | Pension Benefits, Non U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Discount Rate Assumptions Used Calculating Benefit Obligation									4.50%
Expected Long-term Return on Assets Assumptions Used Calculating Net Periodic Benefit Cost									6.20%
After Pension Amendment | Pension Benefits, U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Discount Rate Assumptions Used Calculating Benefit Obligation							5.00%	5.00%
After Pension Amendment | Pension Benefits, Non U.S. Plans
Pension and Other Postretirement Benefits Disclosure
Discount Rate Assumptions Used Calculating Benefit Obligation							4.60%	4.60%
Expected Long-term Return on Assets Assumptions Used Calculating Net Periodic Benefit Cost							6.35%	6.35%
U.S. Defined Contribution Plan
Pension and Other Postretirement Benefits Disclosure
Matching Contribution Percent of Employees' Gross Pay | Rate					5.00%		3.00%	3.00%
Employer Discretionary Contribution Percentage of earnings | Rate					4.50%
Employer Matching Contribution on amts over 3%							$ 0.50
Employer Matching Contribution % for $0.50 | Rate							2.00%	2.00%
Cost Recognized			71,500,000.0			$ 76,000,000	$ 18,800,000.0
Non U.S. Defined Contribution Plan
Pension and Other Postretirement Benefits Disclosure
Matching Contribution Percent of Employees' Gross Pay		5.00%					5.00%	5.00%
Employer Discretionary Contribution Percentage of earnings		6.00%					5.00%	5.00%
Employer Matching Contribution for Every Pound on the First One Percent of Employee Contributions | £				£ 2
Employee Contribution Percentage Received 2-for-1 Employer Match		1.00%
Cost Recognized			$ 5,700,000.0			$ 5,000,000	$ 2,900,000.0