Shareholders' equity Share Repurchases (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Nov. 21, 2019	Dec. 01, 2018
Dec 2018 Stock Repurchase Plan [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount				$ 1,500
Number of shares repurchased		2,753,754
Cost of shares repurchased		$ 367
Repurchase authorization remaining at end of period		$ 1,112
Nov 2019 Stock Repurchase Plan [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount			$ 1,500
Number of shares repurchased	2,266,150
Cost of shares repurchased	$ 326
Repurchase authorization remaining at end of period	$ 1,124