Shareholders' equity Share Repurchases (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 29, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 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			3,079,618		8,417,838
Cost of shares repurchased			$ 478		$ 1,221
Repurchase authorization remaining at end of period			$ 258		$ 258
Nov 2019 Stock Repurchase Plan [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount						$ 1,500
Number of shares repurchased		0		2,266,150
Cost of shares repurchased		$ 0		$ 326
Repurchase authorization remaining at end of period		$ 1,124		$ 1,124
Subsequent Event [Member] | Nov 2019 Stock Repurchase Plan [Member]
Equity, Class of Treasury Stock [Line Items]
Number of shares repurchased	52,500
Cost of shares repurchased	$ 7
Repurchase authorization remaining at end of period	$ 1,117