Fair value measurement (Changes in Contingent Consideration Obligation) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Combination, Contingent Consideration [Roll Forward]
Beginning balance			$ 0	$ 116,000,000
Fair Value, Measurements, Recurring [Member]
Business Combination, Contingent Consideration [Roll Forward]
Beginning balance			69,000,000
Ending balance	$ 66,000,000		66,000,000
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member]
Business Combination, Contingent Consideration [Roll Forward]
Beginning balance	72,000,000	$ 182,000,000	69,000,000	179,000,000
Addition from K-A acquisition	0	0	45,000,000	0
Net changes in valuations	(6,000,000)	(114,000,000)	(48,000,000)	(111,000,000)
Ending balance	$ 66,000,000	$ 68,000,000	$ 66,000,000	$ 68,000,000