Stockholders' equity (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended			3 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2023	Sep. 30, 2022	Mar. 31, 2022	Sep. 30, 2021
Class of Stock [Line Items]
Stock repurchased (in shares)					0.0		24.6
Stock repurchased					$ 0		$ 5,410
Repurchases of common stock						$ 6,310
Amount available for stock repurchases under a board approved stock repurchase plan		$ 7,000		$ 7,000
Dividends declared per share (in usd per share)		$ 2.13	$ 2.13	$ 2.13		$ 1.94
Dividends paid per share (in usd per share)		$ 2.13
Accumulated deficit
Class of Stock [Line Items]
Repurchases of common stock						$ 5,410
Common stock and additional paid-in capital
Class of Stock [Line Items]
Repurchases of common stock						$ 900
Forecast
Class of Stock [Line Items]
Dividends paid per share (in usd per share)	$ 2.13