Treasury stock / share repurchase program (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	1 Months Ended		3 Months Ended	9 Months Ended
	Mar. 31, 2015	Feb. 28, 2015	Oct. 31, 2015	Oct. 31, 2015
Class of Stock [Line Items]
Investment Repurchase Agreement, Date of Agreement				Feb. 05, 2015
Stock Repurchase Program Expiration Date				Dec. 31, 2015
Treasury Stock, Shares	17	28	0	0
Treasury Stock Acquired, Average Cost Per Share	$ 6.27	$ 6.64	$ 0.00
Treasury Stock Acquired, Repurchase Authorization			$ 2	$ 2