Employee Benefit Plans - Additional Information (Detail)	12 Months Ended																								12 Months Ended
	Dec. 31, 2014 USD ($) Rate	Dec. 31, 2014 Pension Benefits, U.S. Plans USD ($)	Dec. 31, 2013 Pension Benefits, U.S. Plans USD ($)	Dec. 31, 2012 Pension Benefits, U.S. Plans USD ($)	Dec. 31, 2014 Pension Benefits, Non U.S. Plans USD ($)	Dec. 31, 2014 Pension Benefits, Non U.S. Plans GBP (£)	Dec. 31, 2013 Pension Benefits, Non U.S. Plans USD ($) Rate	Dec. 31, 2013 Pension Benefits, Non U.S. Plans GBP (£) Rate	Dec. 31, 2012 Pension Benefits, Non U.S. Plans USD ($) Rate	Dec. 31, 2014 Other Postretirement Benefit Plans	Dec. 31, 2014 Other Postretirement Benefit Plans USD ($)	Dec. 31, 2013 Other Postretirement Benefit Plans USD ($) Rate	Dec. 31, 2012 Other Postretirement Benefit Plans USD ($)	Dec. 31, 2014 Equity Securites Pension Benefits, U.S. Plans Rate	Dec. 31, 2014 Fixed Maturity Securities Pension Benefits, U.S. Plans Rate	Dec. 31, 2014 Alternative Investments Pension Benefits, U.S. Plans Rate	Dec. 31, 2014 Diversified Growth Assets Pension Benefits, Non U.S. Plans Rate	Dec. 31, 2014 Interest Rate Contract Pension Benefits, Non U.S. Plans Rate	Dec. 31, 2014 Minimum	Dec. 31, 2014 Minimum Private Equity Funds Pension Benefits, U.S. Plans	Dec. 31, 2014 Maximum	Dec. 31, 2014 Maximum Private Equity Funds Pension Benefits, U.S. Plans	Dec. 31, 2012 Prior to Pension Amendments Pension Benefits, Non U.S. Plans	Dec. 31, 2013 After Pension Amendment Pension Benefits, U.S. Plans	Dec. 31, 2013 After Pension Amendment Pension Benefits, Non U.S. Plans	Dec. 31, 2013 Pre-Remeasurement Date Pension Benefits, U.S. Plans	Dec. 31, 2013 Pre-Remeasurement Date Pension Benefits, Non U.S. Plans	Dec. 31, 2013 Post-Remeasurement Date Pension Benefits, U.S. Plans	Dec. 31, 2013 Post-Remeasurement Date Pension Benefits, Non U.S. Plans	Dec. 31, 2014 U.S. Defined Contribution Plan USD ($)	Dec. 31, 2013 U.S. Defined Contribution Plan USD ($) Rate	Dec. 31, 2012 U.S. Defined Contribution Plan USD ($)	Dec. 31, 2014 Non U.S. Defined Contribution Plan USD ($)	Dec. 31, 2014 Non U.S. Defined Contribution Plan GBP (£)	Dec. 31, 2013 Non U.S. Defined Contribution Plan USD ($)	Dec. 31, 2012 Non U.S. Defined Contribution Plan USD ($)
Pension and Other Postretirement Benefits Disclosure
Pension Plan Lump-sum Settlement Payment		$ 214,500,000	$ 0		$ 0		$ 0				$ 0	$ 0
Pension Settlement Costs		64,400,000	0	0	0		0		0		0	0	0
Discount Rate Assumptions Used Calculating Benefit Obligation		4.40%	5.30%		3.60%	3.60%	4.40%	4.40%		4.30%	4.30%	5.00%											4.50%	5.00%	4.60%
Expected Long-term Return on Assets Assumptions Used Calculating Net Periodic Benefit Cost		7.50%	7.50%		6.10%	6.10%				5.75%	5.75%	5.75%											6.20%		6.35%		6.20%		6.35%
Decrease in Pension Liability Due to Remeasurement			327,400,000				2,300,000	1,500,000
Tax Impact of Curtailments			114,600,000
Recognized Net Gain (Loss) Due to Curtailments		0	(700,000)	0	0		3,700,000	2,300,000	0		0	0	0
Defined Benefit Plan, Curtailments		0	126,800,000		0		3,700,000				0	0	4,200,000
Maximum Inflation Rate on Pensionable Earnings							2.50%	2.50%	5.00%
Net Prior Service Credit Recognized in Other Comprehensive Income Before Tax													5,000,000
Average Remaining Life Expectancy of Plan Participants		35 years			34 years	34 years
Target Plan Asset Allocations														35.00%	40.00%	25.00%	75.00%	25.00%
Private Equity Partnership Future Liquidation Term																			1 year	5 years	13 years	8 years
Level 3 Transfers Into	0										0
Level 3 Transfers Out of											0
Discount Rate Assumptions Used Calculating Net Periodic Benefit Cost		5.30%			4.40%	4.40%				5.00%	5.00%	4.20%														4.50%	4.50%	5.00%	4.60%
Interest Rate During Period										5.46%	5.46%	5.58%
Health Care Cost Trend Rate Assumed for Next Fiscal Year	7.50%											7.50%
Ultimate Health Care Cost Trend Rate	5.00%
Effect of One Percentage Point Increase on Service and Interest Cost Components	100,000
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	4,700,000
Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation	(3,400,000)
Net Actuarial Loss to be Amortized from Accumulated Other Comprehensive Income Next Fiscal Year	11,900,000
General Discussion of Pension and Other Postretirement Benefits		We had no regulatory contribution requirements for our U.S. qualified defined benefit plan in 2014
Employer Contributions to Defined Benefit Plan		5,300,000	54,700,000		2,300,000	1,400,000	4,000,000				12,000,000	11,700,000
Contributions Percent of Pensionable Earnings							30.00%	30.00%	24.80%
Matching Contribution Percent of Employees' Gross Pay																														5.00%	3.00%		5.00%	5.00%	5.00%
Employer Discretionary Contribution Percentage of earnings																														4.50%			6.00%	6.00%	5.00%
Employer Matching Contribution on amts over 3%																															0.50
Employer Matching Contribution % for $0.50																															2.00%
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%	1.00%
Cost Recognized																														$ 76,000,000	$ 18,800,000.0	$ 18,900,000.0	$ 5,000,000		$ 2,900,000.0	$ 2,900,000.0