Derivatives Designated as Hedging Instruments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Other Financial Items, net
Interest Expense	0		0	0		0
Interest Income
Amount of gain (loss) recognized in OCI on derivative effective portion
Amount of gain (loss) reclassified from accumulated OCI into interest expense
Fair Value Hedge | Fixed Rate Private Placement Debt Due 2019
Derivative Instruments, Gain (Loss) [Line Items]
Nominal Volume			60.0			60.0
Other Financial Items, net
Interest Expense			(1.5)	1.3		(0.9)
Interest Income
Amount of gain (loss) recognized in OCI on derivative effective portion
Amount of gain (loss) reclassified from accumulated OCI into interest expense
Derivatives Designated as Hedging Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Nominal Volume			60.0			60.0
Other Financial Items, net
Interest Income
Amount of gain (loss) recognized in OCI on derivative effective portion
Amount of gain (loss) reclassified from accumulated OCI into interest expense
Derivatives Designated as Hedging Instruments | Fair Value Hedge | Interest Rate Swaps | Less Than 7 Years
Derivative Instruments, Gain (Loss) [Line Items]
Other Financial Items, net		[1]			[1]
Interest Expense				(1.3)	[1]
Interest Income		[1]			[1]
Amount of gain (loss) recognized in OCI on derivative effective portion		[1]			[1]
Amount of gain (loss) reclassified from accumulated OCI into interest expense		[1]			[1]
Derivatives Designated as Hedging Instruments | Fair Value Hedge | Interest Rate Swaps | Less Than 8 Years
Derivative Instruments, Gain (Loss) [Line Items]
Nominal Volume			60.0			60.0
Other Financial Items, net
Interest Expense			1.5			0.9
Interest Income
Amount of gain (loss) recognized in OCI on derivative effective portion
Amount of gain (loss) reclassified from accumulated OCI into interest expense

[1] The decrease from year end is explained by the closure of a $60 million interest rate swap in Q1 of 2013.