US Changes in Assets measured at fair value using signifcant unobservable inputs (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Beginning of Year	$ 1,025.7	$ 869.4
Purchases	228.3	105.3
Sales	(84.7)	(70.1)
Level 3 Transfers Into	561.9	565.1
Level 3 Transfers Out of	(626.3)	(503.8)
End of Year	1,141.4	1,025.7
Pension Benefits, U.S. Plans | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning of Year	61.0	46.0
Actual Return on Plan Assets Held at Year End	1.4	3.4
Actual Return on Plan Assets Sold During the Year	(0.1)	0
Purchases	13.4	11.6
Sales	(7.7)	0
Level 3 Transfers Into	0	0
Level 3 Transfers Out of	0	0
End of Year	68.0	61.0
Pension Benefits, U.S. Plans | Private Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning of Year	15.0	8.2
Actual Return on Plan Assets Held at Year End	3.0	0.6
Actual Return on Plan Assets Sold During the Year	0	0
Purchases	6.5	6.2
Sales	(0.8)	0
Level 3 Transfers Into	0	0
Level 3 Transfers Out of	0	0
End of Year	23.7	15.0
Pension Benefits, U.S. Plans | Hedge Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning of Year	46.0	37.8
Actual Return on Plan Assets Held at Year End	(1.6)	2.8
Actual Return on Plan Assets Sold During the Year	(0.1)	0
Purchases	6.9	5.4
Sales	(6.9)	0
Level 3 Transfers Into	0	0
Level 3 Transfers Out of	0	0
End of Year	$ 44.3	$ 46.0