Business combinations (Aggregate Consideration Paid - Dezima) (Details) - Dezima [Member] - USD ($) $ in Millions		12 Months Ended
	Oct. 14, 2015	Dec. 31, 2015
Business Acquisition [Line Items]
Total cash paid to former shareholders of Dezima	$ 300
Fair value of contingent consideration obligations	110	$ 110
Total consideration	$ 410