(Financial Assets and Liabilities Measured at Fair Value on Recurring Basis) (Detail) (Fair Value, Measurements, Recurring, USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	$ 189.0
Derivative assets	211.8
Total assets at fair value	400.8
Derivative liabilities	(158.1)
Total liabilities at fair value	(158.1)
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	189.0
Derivative assets	137.9
Total assets at fair value	326.9
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	73.9
Total assets at fair value	73.9
Derivative liabilities	(158.1)
Total liabilities at fair value	$ (158.1)