Shareholders' equity Share Repurchases (Details) - Nov 2016 Stock Repurchase Plan [Member] - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	May 04, 2017	Mar. 31, 2017
Class of Stock [Line Items]
Treasury Stock, Shares, Acquired		1,036,064
Treasury Stock, Value, Acquired, Cost Method		$ 140
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 860
Subsequent Event [Member]
Class of Stock [Line Items]
Treasury Stock, Shares, Acquired	664,301
Treasury Stock, Value, Acquired, Cost Method	$ 91
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 769