Stockholders' equity (Stock Repurchase Program) (Details) - USD ($) shares in Millions	3 Months Ended												12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Oct. 31, 2021
Equity [Abstract]
Stock repurchases, Shares	6.9	4.6	6.5	3.7	5.3	3.0	2.6	4.3	5.1	6.2	13.1	15.9	21.7	15.2	40.2
Stock repurchases	$ 1,461,000,000	$ 1,069,000,000	$ 1,592,000,000	$ 865,000,000	$ 1,221,000,000	$ 752,000,000	$ 591,000,000	$ 933,000,000	$ 1,090,000,000	$ 1,170,000,000	$ 2,349,000,000	$ 3,031,000,000	$ 4,987,000,000	$ 3,497,000,000	$ 7,640,000,000
Stock repurchase program, additional authorized amount	5,000,000,000			$ 3,400,000,000									5,000,000,000			$ 4,500,000,000
Amount available for stock repurchases under a board approved stock repurchase plan	$ 10,900,000,000												$ 10,900,000,000