Income Tax Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Line Items]
Original UK Tax rate	28.00%
Ultimate UK Tax rate	21.00%
Income Tax Reconciliation, Change in Enacted Tax Rate	$ 9.3	$ 6.8	$ 2.7
UK Tax Rate Change, percent	2.00%		1.00%
Deferred Tax Liability Not Recognized, Amount of Unrecognized Deferred Tax Liability	992.2
Liability for unrecognized tax benefits	15.0	86.9	123.7
Interest expense and penalties related to unrecognized tax expense	(10.4)	(13.1)	5.5
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	1.9	12.3	25.4
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority	60.4
Income Tax Examination, Increase (Decrease) in Liability from Prior Year	(11.0)	(41.3)
Other Noncash Income Tax Expense			10.2
Operating Loss Carryforwards	0
Valuation Allowance, Deferred Tax Asset, Change in Amount		4.1
Income Taxes Paid, Net	185.0	303.5	273.0
Before Tax [Member]
Income Taxes [Line Items]
Income Tax Examination, Interest from Examination		17.5
After Tax [Member]
Income Taxes [Line Items]
Income Tax Examination, Interest from Examination		11.4
Minimum [Member]
Income Taxes [Line Items]
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority	0
Maximum [Member]
Income Taxes [Line Items]
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority	$ 10.0