Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) (Fair Value, Measurements, Recurring, USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 405.7		$ 722.5
Investments	126.4		131.6
Derivative assets	203.2		192.9
Total assets at fair value	735.3		1,047.0
Derivative liabilities	(11.1)		(8.4)
Total liabilities at fair value	(11.1)		(8.4)
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	405.7		722.5
Investments	126.4	[1]	131.6	[1]
Derivative assets	132.6	[1]	104.4	[1]
Total assets at fair value	664.7		958.5
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	70.6		88.5
Total assets at fair value	70.6		88.5
Derivative liabilities	(11.1)		(8.4)
Total liabilities at fair value	$ (11.1)		$ (8.4)

[1] Includes investments and derivatives that hedge market-driven changes in liabilities associated with the Company's supplemental benefit plans.