Impact of Rights of Offset Associated with Recognized Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Current Asset [Member]
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Assets	$ 14.4
Long-term assets [Member]
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Assets	5.1
Current liabilities [Member]
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Liabilities	(8.3)
Long-term liabilities [Member]
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Liabilities	(0.3)
Effects of Netting [Member] | Current Asset [Member]
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Assets	(5.0)
Effects of Netting [Member] | Long-term assets [Member]
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Assets	(3.5)
Effects of Netting [Member] | Current liabilities [Member]
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Liabilities	8.2
Effects of Netting [Member] | Long-term liabilities [Member]
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Liabilities	0.3
With Effects of Netting [Member] | Current Asset [Member]
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Assets	9.4
With Effects of Netting [Member] | Long-term assets [Member]
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Assets	1.6
With Effects of Netting [Member] | Current liabilities [Member]
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Liabilities	(0.1)
With Effects of Netting [Member] | Long-term liabilities [Member]
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Liabilities