Summary of Fair value of Plan Assets by Asset Category (Parenthetical) (Detail) (UNITED KINGDOM)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Cash | Balanced Fund
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	3.00%	7.00%
Cash | Growth Funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	1.00%	6.00%
Equity Securities | Balanced Fund
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	47.00%	40.00%
Equity Securities | Growth Funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	68.00%	60.00%
Debt Securities | Balanced Fund
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	41.00%	36.00%
Debt Securities | Growth Funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	21.00%	18.00%
Other Assets | Balanced Fund
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	9.00%	17.00%
Other Assets | Growth Funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, target plan asset allocations	10.00%	16.00%