Debt - long-term debt (Details)	Aug. 31, 2019 USD ($)	Aug. 31, 2019 EUR (€)	Aug. 31, 2019 GBP (£)	Aug. 31, 2018 USD ($)
Long-Term Debt [Abstract]
Other	$ 25,000,000			$ 23,000,000
Total long-term debt, less current portion	11,098,000,000			12,431,000,000
3.450% unsecured notes due 2026 | Unsecured Debt
Long-Term Debt [Abstract]
Carrying value of notes, net of unamortized discount and interest rate swap FMV adjustment	$ 1,890,000,000			1,888,000,000
Stated interest rate (as a percent)	3.45%	3.45%	3.45%
4.650% unsecured notes due 2046 | Unsecured Debt
Long-Term Debt [Abstract]
Carrying value of notes, net of unamortized discount and interest rate swap FMV adjustment	$ 591,000,000			590,000,000
Stated interest rate (as a percent)	4.65%	4.65%	4.65%
2.700% unsecured notes due 2019 | Unsecured Debt
Long-Term Debt [Abstract]
Carrying value of notes, net of unamortized discount and interest rate swap FMV adjustment	$ 0			1,248,000,000
Stated interest rate (as a percent)	2.70%	2.70%	2.70%
3.300% unsecured notes due 2021 | Unsecured Debt
Long-Term Debt [Abstract]
Carrying value of notes, net of unamortized discount and interest rate swap FMV adjustment	$ 1,247,000,000			1,245,000,000
Stated interest rate (as a percent)	3.30%	3.30%	3.30%
3.800% unsecured notes due 2024 | Unsecured Debt
Long-Term Debt [Abstract]
Carrying value of notes, net of unamortized discount and interest rate swap FMV adjustment	$ 1,992,000,000			1,990,000,000
Stated interest rate (as a percent)	3.80%	3.80%	3.80%
4.500% unsecured notes due 2034 | Unsecured Debt
Long-Term Debt [Abstract]
Carrying value of notes, net of unamortized discount and interest rate swap FMV adjustment	$ 495,000,000			495,000,000
Stated interest rate (as a percent)	4.50%	4.50%	4.50%
4.800% unsecured notes due 2044 | Unsecured Debt
Long-Term Debt [Abstract]
Carrying value of notes, net of unamortized discount and interest rate swap FMV adjustment	$ 1,492,000,000			1,492,000,000
Stated interest rate (as a percent)	4.80%	4.80%	4.80%
2.875% unsecured Pound sterling notes due 2020 | Unsecured Debt
Long-Term Debt [Abstract]
Carrying value of notes, net of unamortized discount and interest rate swap FMV adjustment	$ 488,000,000			517,000,000
Stated interest rate (as a percent)	2.875%	2.875%	2.875%
3.600% unsecured Pound sterling notes due 2025 | Unsecured Debt
Long-Term Debt [Abstract]
Carrying value of notes, net of unamortized discount and interest rate swap FMV adjustment	$ 365,000,000			387,000,000
Stated interest rate (as a percent)	3.60%	3.60%	3.60%
2.125% unsecured Euro notes due 2026 | Unsecured Debt
Long-Term Debt [Abstract]
Carrying value of notes, net of unamortized discount and interest rate swap FMV adjustment	$ 824,000,000			868,000,000
Stated interest rate (as a percent)	2.125%	2.125%	2.125%
3.100% unsecured notes due 2022 | Unsecured Debt
Long-Term Debt [Abstract]
Carrying value of notes, net of unamortized discount and interest rate swap FMV adjustment	$ 1,197,000,000			1,196,000,000
Stated interest rate (as a percent)	3.10%	3.10%	3.10%
4.400% unsecured notes due 2042 | Unsecured Debt
Long-Term Debt [Abstract]
Carrying value of notes, net of unamortized discount and interest rate swap FMV adjustment	$ 493,000,000			$ 492,000,000
Stated interest rate (as a percent)	4.40%	4.40%	4.40%
Total $6.0 billion debt issuance
Long-Term Debt [Abstract]
Face amount	$ 6,000,000,000
Fair value of the notes	2,600,000,000
Carrying value of notes	2,500,000,000
Total $8.0 billion debt Issuance
Long-Term Debt [Abstract]
Face amount	8,000,000,000
Fair value of the notes	6,800,000,000
Carrying value of notes	6,500,000,000
Total 700 million pounds debt issuance
Long-Term Debt [Abstract]
Face amount | £			£ 700,000,000
Fair value of the notes	900,000,000
Carrying value of notes	900,000,000
Total 750 million euros debt issuance
Long-Term Debt [Abstract]
Face amount | €		€ 750,000,000
Fair value of the notes	900,000,000
Carrying value of notes	800,000,000
Total $4.0 billion debt issuance
Long-Term Debt [Abstract]
Face amount	4,000,000,000
Fair value of the notes	1,700,000,000
Carrying value of notes	$ 1,700,000,000