Debt - long-term debt (Details)	Oct. 20, 2020 GBP (£)	Aug. 31, 2020 USD ($)	Aug. 31, 2020 GBP (£)	Aug. 31, 2020 EUR (€)	Apr. 15, 2020 USD ($)	Aug. 31, 2019 USD ($)
Long-Term Debt [Abstract]
Other		$ 24,000,000				$ 25,000,000
Total long-term debt, less current portion		12,203,000,000				11,098,000,000
Total $1.5 billion debt issuance
Long-Term Debt [Abstract]
Face amount					$ 1,500,000,000
Total $1.5 billion debt issuance | Unsecured Debt
Long-Term Debt [Abstract]
Face amount		1,500,000,000
3.200% unsecured notes due 2030 | Unsecured Debt
Long-Term Debt [Abstract]
Carrying value of notes, net of unamortized discount and interest rate swap FMV adjustment		$ 497,000,000				0
Stated interest rate (as a percent)		3.20%	3.20%	3.20%	3.20%
Face amount					$ 500,000,000
4.100% unsecured notes due 2050 | Unsecured Debt
Long-Term Debt [Abstract]
Carrying value of notes, net of unamortized discount and interest rate swap FMV adjustment		$ 990,000,000				0
Stated interest rate (as a percent)		4.10%	4.10%	4.10%	4.10%
Face amount					$ 1,000,000,000.0
Total $6.0 billion debt issuance | Unsecured Debt
Long-Term Debt [Abstract]
Face amount		$ 6,000,000,000
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		$ 1,891,000,000				1,890,000,000
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				591,000,000
Stated interest rate (as a percent)		4.65%	4.65%	4.65%
Total $8.0 billion debt Issuance | Unsecured Debt
Long-Term Debt [Abstract]
Face amount		$ 8,000,000,000
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		$ 1,248,000,000				1,247,000,000
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		$ 1,993,000,000				1,992,000,000
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		$ 496,000,000				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		$ 1,493,000,000				1,492,000,000
Stated interest rate (as a percent)		4.80%	4.80%	4.80%
Total 700 million pounds debt issuance | Unsecured Debt
Long-Term Debt [Abstract]
Face amount | £			£ 700,000,000
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		$ 0				488,000,000
Stated interest rate (as a percent)		2.875%	2.875%	2.875%
2.875% unsecured Pound sterling notes due 2020 | Unsecured Debt | Forecast
Long-Term Debt [Abstract]
Debt expected to be redeemed | £	£ 400,000,000
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		$ 398,000,000				365,000,000
Stated interest rate (as a percent)		3.60%	3.60%	3.60%
Total 750 million euros debt issuance | Unsecured Debt
Long-Term Debt [Abstract]
Face amount | €				€ 750,000,000
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		$ 891,000,000				824,000,000
Stated interest rate (as a percent)		2.125%	2.125%	2.125%
Total $4.0 billion debt issuance | Unsecured Debt
Long-Term Debt [Abstract]
Face amount		$ 4,000,000,000
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		$ 1,198,000,000				1,197,000,000
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				$ 493,000,000
Stated interest rate (as a percent)		4.40%	4.40%	4.40%