Employee Benefit Plans - Additional Information (Detail)	12 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended	3 Months Ended					6 Months Ended	9 Months Ended		12 Months Ended	9 Months Ended	12 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2013 USD ($)	Jun. 30, 2013 Pension Benefits, U.S. Plans USD ($)	Sep. 30, 2013 Pension Benefits, U.S. Plans	Dec. 31, 2012 Pension Benefits, U.S. Plans	Dec. 31, 2013 Foreign Pension Plans, U.K. Plan Rate	Sep. 30, 2013 Foreign Pension Plans, U.K. Plan USD ($) Rate	Sep. 30, 2013 Foreign Pension Plans, U.K. Plan GBP (£) Rate	Jun. 30, 2013 Foreign Pension Plans, U.K. Plan USD ($) Rate	Jun. 30, 2013 Foreign Pension Plans, U.K. Plan GBP (£) Rate	Jun. 30, 2013 Foreign Pension Plans, U.K. Plan Rate	Sep. 30, 2013 Foreign Pension Plans, U.K. Plan USD ($) Rate	Sep. 30, 2013 Foreign Pension Plans, U.K. Plan GBP (£) Rate	Dec. 31, 2012 Foreign Pension Plans, U.K. Plan	Sep. 30, 2013 UNITED STATES Defined Contribution Pension USD ($)	Dec. 31, 2014 UNITED STATES Defined Contribution Pension	Dec. 31, 2014 UNITED KINGDOM Defined Contribution Pension GBP (£) Rate	Sep. 30, 2013 UNITED KINGDOM Defined Contribution Pension	Dec. 31, 2014 UNITED KINGDOM Defined Contribution Pension
Pension and Other Postretirement Benefits Disclosure
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		5.00%		4.50%		4.60%	4.60%				4.60%	4.60%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets			7.50%	7.50%		6.35%	6.35%			6.20%
Before-tax Change in Pension Liability Due to Pension Plan Amendment		$ (327,400,000)				$ (2,300,000)	£ (1,500,000)
Defined Benefit Plan, Income Tax on Change in AOCI due to US Pension Plan Amendment		(114,600,000)
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments		(700,000)						3,700,000	2,300,000
Description of Contribution Requirements on Defined Contribution Pension Plan			We have no regulatory contribution requirements for our U.S. qualified defined benefit plan in 2013
Pension Contributions		50,000,000				900,000	600,000				2,800,000	1,800,000
Maximum Inflation Rate on Pensionable Earnings						2.50%	2.50%	5.00%	5.00%	5.00%	2.50%	2.50%
Pension Plan Contributions, Percent of Pensionable Earnings					30.00%						24.80%	24.80%
Average Remaining Life Expectancy of Plan Participants		30 years				35 years	35 years						11 years
Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Current Fiscal Year	28,100,000
Pension, Amount that will be recognized from AOCI to Income, after tax	18,500,000
Defined Contribution Plan, Employer Matching Contribution, Percent														3.00%	5.00%		5.00%	5.00%
Defined Contribution Plan, Employer Matching Contribution on amts over 3%														0.50
Defined Contribution Plan, Employer Matching Contribution % for $0.50														2.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount															4.50%	6.00%	5.00%
Defined Contribution Plan, Employer Matching Contribution for Every Pound on the First One Percent of Employee Contributions																£ 2
Defined Contribution Plan, Employee Contribution Percentage Received 2-for-1 Employer Match																1.00%