Equity method investments - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended					9 Months Ended
	May 11, 2022	May 31, 2022	Feb. 28, 2022	Nov. 30, 2021	May 31, 2021	Sep. 30, 2020	May 31, 2022	May 31, 2021	Aug. 31, 2021
Schedule of Equity Method Investments [Line Items]
Gain on sale of equity method investment							$ 421	$ 290
Equity earnings (loss)							359	(577)
Impairment of equity method investments and investments in debt and equity securities							233	0
Share of OCI of equity method investments
Schedule of Equity Method Investments [Line Items]
Loss associated with sale of equity method investment reclassified within accumulated other comprehensive income		$ 48			$ (2)		$ 213	(21)
AmerisourceBergen
Schedule of Equity Method Investments [Line Items]
Number of share sold (in shares)	6,000,000
Share price of stock sold (in dollars per share)	$ 150
Proceeds from sale of equity method investment	$ 900
Outstanding shares owned (in shares)		52,854,867					52,854,867		58,854,867
Gain on sale of equity method investment	424
Outstanding vested equity interest percentage		25.20%					25.20%		28.00%
Period of reporting lag							2 months
Equity earnings (loss)					(1,200)		$ 330
Equity investment, exceeded its proportionate share of net assets		$ 3,800					3,800
AmerisourceBergen | Share of OCI of equity method investments
Schedule of Equity Method Investments [Line Items]
Loss associated with sale of equity method investment reclassified within accumulated other comprehensive income	$ 25
AmerisourceBergen | Opiod Litigation
Schedule of Equity Method Investments [Line Items]
Equity earnings (loss)						$ (5,600)
AmerisourceBergen | Level 1
Schedule of Equity Method Investments [Line Items]
Fair market value of equity investment		8,200					8,200		$ 7,200
Other Investments
Schedule of Equity Method Investments [Line Items]
Equity earnings (loss)		$ 5			575		$ 29	604
VillageMD
Schedule of Equity Method Investments [Line Items]
Gain on sale of equity method investment				$ 2,200
Shields Health Solutions Parent, LLC
Schedule of Equity Method Investments [Line Items]
Gain on sale of equity method investment				$ 402
Investments in China
Schedule of Equity Method Investments [Line Items]
Impairment of equity method investments and investments in debt and equity securities			$ 124
Option Care Health
Schedule of Equity Method Investments [Line Items]
Gain on sale of equity method investment					98			290
Equity earnings (loss)					$ 576
Option Care Health | HC Group Holdings I, LLC
Schedule of Equity Method Investments [Line Items]
Gain on sale of equity method investment								$ 1,200