Financial instruments and risk concentration (Tables)

12 Months Ended

Dec. 31, 2012

Risks and Uncertainties [Abstract]

Allowance for losses based on the expected collectability of accounts receivable

Details of these Accounts receivable allowances are as follows:

Accounts receivable allowances	Balance at Beginning of Year		Additions Charged (Credited) to Operating Results			Recoveries and Write-offs, Net			Balance at End of Year
2012	$	19	$	12		$	—		$	31
2011	18		1			—			19
2010	23		(4		)	(1		)	18