Income Tax Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Taxes [Line Items]
Original UK Tax rate	28.00%
Ultimate UK Tax rate	23.00%
2010 UK Tax Rate	27.00%
2011 New UK Tax rate	26.00%
2012 UK tax rate	25.00%
Income Tax Reconciliation, Change in Enacted Tax Rate	$ 6.8	$ 2.7
Deferred Tax Liability Not Recognized, Amount of Unrecognized Deferred Tax Liability	884.2	1,027.7
Liability for unrecognized tax benefits	86.9	123.7	131.6
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	12.3	25.4	19.9
Interest expense and penalties related to unrecognized tax expense	13.1	(5.5)	(6.5)
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority	60.0
Income Tax Examination, Increase (Decrease) in Liability from Prior Year	(41.3)
Other Noncash Income Tax Expense		10.2
Operating Loss Carryforwards	0
Valuation Allowance, Amount	0	4.1
Valuation Allowance, Deferred Tax Asset, Change in Amount	4.1
Income Taxes Paid, Net	303.5	273.0	381.6
Before Tax [Member]
Income Taxes [Line Items]
Income Tax Examination, Interest from Examination	17.5		0.3
After Tax [Member]
Income Taxes [Line Items]
Income Tax Examination, Interest from Examination	11.4		0.2
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	$ 73.0