Impact of Rights of Offset Associated with Recognized Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
Current Asset
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Assets	$ 30.1
Long-term assets
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Assets	13.2
Current liabilities
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Liabilities	(1.9)
Long-term liabilities
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Liabilities	(0.4)
Effects of Netting | Current Asset
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Assets	(1.8)
Effects of Netting | Long-term assets
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Assets	(0.5)
Effects of Netting | Current liabilities
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Liabilities	1.9
Effects of Netting | Long-term liabilities
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Liabilities	0.4
With Effects of Netting | Current Asset
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Assets	28.3
With Effects of Netting | Long-term assets
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Assets	12.7
With Effects of Netting | Current liabilities
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Liabilities
With Effects of Netting | Long-term liabilities
Derivative Instruments And Hedging Activities [Line Items]
Fair Value of Derivative Instruments, Liabilities