Shareholders' equity Share Repurchases (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 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		2,584,466		5,338,220
Cost of shares repurchased		$ 376		$ 743
Repurchase authorization remaining at end of period		$ 736		$ 736
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