Debt - Summary of Term Debt (Details)	12 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2017 CAD	Sep. 30, 2017 EUR (€)	Sep. 24, 2016 USD ($)
Debt Instrument [Line Items]
Total term debt	$ 104,021,000,000			$ 78,384,000,000
Unamortized premium/(discount) and issuance costs, net	(225,000,000)			(174,000,000)
Hedge accounting fair value adjustments	(93,000,000)			717,000,000
Less: Current portion of long-term debt	(6,496,000,000)			(3,500,000,000)
Total long-term debt	97,207,000,000			75,427,000,000
2013 debt issuance of $17.0 billion
Debt Instrument [Line Items]
Debt instrument, face amount	17,000,000,000
2013 debt issuance of $17.0 billion | Floating-rate notes
Debt Instrument [Line Items]
Total term debt	$ 2,000,000,000			$ 2,000,000,000
Debt instrument maturity year, start	2018
Debt instrument maturity year, end	2018
2013 debt issuance of $17.0 billion | Floating-rate notes | Minimum
Debt Instrument [Line Items]
Debt instrument, effective interest rate	1.10%	1.10%	1.10%	1.10%
2013 debt issuance of $17.0 billion | Floating-rate notes | Maximum
Debt Instrument [Line Items]
Debt instrument, effective interest rate	1.10%	1.10%	1.10%	1.10%
2013 debt issuance of $17.0 billion | Fixed-rate 1.000% – 3.850% notes
Debt Instrument [Line Items]
Total term debt	$ 12,500,000,000			$ 12,500,000,000
Debt instrument maturity year, start	2018
Debt instrument maturity year, end	2043
2013 debt issuance of $17.0 billion | Fixed-rate 1.000% – 3.850% notes | Minimum
Debt Instrument [Line Items]
Debt instrument, stated interest rate	1.00%	1.00%	1.00%
Debt instrument, effective interest rate	1.08%	1.08%	1.08%	1.08%
2013 debt issuance of $17.0 billion | Fixed-rate 1.000% – 3.850% notes | Maximum
Debt Instrument [Line Items]
Debt instrument, stated interest rate	3.85%	3.85%	3.85%
Debt instrument, effective interest rate	3.91%	3.91%	3.91%	3.91%
2014 debt issuance of $12.0 billion
Debt Instrument [Line Items]
Debt instrument, face amount	$ 12,000,000,000
2014 debt issuance of $12.0 billion | Floating-rate notes
Debt Instrument [Line Items]
Total term debt	$ 1,000,000,000			$ 2,000,000,000
Debt instrument maturity year, start	2019
Debt instrument maturity year, end	2019
2014 debt issuance of $12.0 billion | Floating-rate notes | Minimum
Debt Instrument [Line Items]
Debt instrument, effective interest rate	1.61%	1.61%	1.61%	0.86%
2014 debt issuance of $12.0 billion | Floating-rate notes | Maximum
Debt Instrument [Line Items]
Debt instrument, effective interest rate	1.61%	1.61%	1.61%	1.09%
2014 debt issuance of $12.0 billion | Fixed-rate 2.100% – 4.450% notes
Debt Instrument [Line Items]
Total term debt	$ 8,500,000,000			$ 10,000,000,000
Debt instrument maturity year, start	2019
Debt instrument maturity year, end	2044
2014 debt issuance of $12.0 billion | Fixed-rate 2.100% – 4.450% notes | Minimum
Debt Instrument [Line Items]
Debt instrument, stated interest rate	2.10%	2.10%	2.10%
Debt instrument, effective interest rate	1.61%	1.61%	1.61%	0.85%
2014 debt issuance of $12.0 billion | Fixed-rate 2.100% – 4.450% notes | Maximum
Debt Instrument [Line Items]
Debt instrument, stated interest rate	4.45%	4.45%	4.45%
Debt instrument, effective interest rate	4.48%	4.48%	4.48%	4.48%
2015 debt issuances of $27.3 billion
Debt Instrument [Line Items]
Debt instrument, face amount	$ 27,300,000,000
2015 debt issuances of $27.3 billion | Floating-rate notes
Debt Instrument [Line Items]
Total term debt	$ 1,549,000,000			$ 1,781,000,000
Debt instrument maturity year, start	2019
Debt instrument maturity year, end	2020
2015 debt issuances of $27.3 billion | Floating-rate notes | Minimum
Debt Instrument [Line Items]
Debt instrument, effective interest rate	1.56%	1.56%	1.56%	0.87%
2015 debt issuances of $27.3 billion | Floating-rate notes | Maximum
Debt Instrument [Line Items]
Debt instrument, effective interest rate	1.87%	1.87%	1.87%	1.87%
2015 debt issuances of $27.3 billion | Fixed-rate 0.350% – 4.375% notes
Debt Instrument [Line Items]
Total term debt	$ 24,522,000,000			$ 25,144,000,000
Debt instrument maturity year, start	2019
Debt instrument maturity year, end	2045
2015 debt issuances of $27.3 billion | Fixed-rate 0.350% – 4.375% notes | Minimum
Debt Instrument [Line Items]
Debt instrument, stated interest rate	0.35%	0.35%	0.35%
Debt instrument, effective interest rate	0.28%	0.28%	0.28%	0.28%
2015 debt issuances of $27.3 billion | Fixed-rate 0.350% – 4.375% notes | Maximum
Debt Instrument [Line Items]
Debt instrument, stated interest rate	4.375%	4.375%	4.375%
Debt instrument, effective interest rate	4.51%	4.51%	4.51%	4.51%
2016 debt issuances of $24.9 billion
Debt Instrument [Line Items]
Debt instrument, face amount	$ 24,900,000,000
2016 debt issuances of $24.9 billion | Floating-rate notes
Debt Instrument [Line Items]
Total term debt	$ 1,350,000,000			$ 1,350,000,000
Debt instrument maturity year, start	2019
Debt instrument maturity year, end	2021
2016 debt issuances of $24.9 billion | Floating-rate notes | Minimum
Debt Instrument [Line Items]
Debt instrument, effective interest rate	1.45%	1.45%	1.45%	0.91%
2016 debt issuances of $24.9 billion | Floating-rate notes | Maximum
Debt Instrument [Line Items]
Debt instrument, effective interest rate	2.44%	2.44%	2.44%	1.95%
2016 debt issuances of $24.9 billion | Fixed-rate 1.100% – 4.650% notes
Debt Instrument [Line Items]
Total term debt	$ 23,645,000,000			$ 23,609,000,000
Debt instrument maturity year, start	2018
Debt instrument maturity year, end	2046
2016 debt issuances of $24.9 billion | Fixed-rate 1.100% – 4.650% notes | Minimum
Debt Instrument [Line Items]
Debt instrument, stated interest rate	1.10%	1.10%	1.10%
Debt instrument, effective interest rate	1.13%	1.13%	1.13%	1.13%
2016 debt issuances of $24.9 billion | Fixed-rate 1.100% – 4.650% notes | Maximum
Debt Instrument [Line Items]
Debt instrument, stated interest rate	4.65%	4.65%	4.65%
Debt instrument, effective interest rate	4.78%	4.78%	4.78%	4.58%
Second quarter 2017 debt issuance of $10.0 billion
Debt Instrument [Line Items]
Debt instrument, face amount	$ 10,000,000,000
Second quarter 2017 debt issuance of $10.0 billion | Floating-rate notes due 2019
Debt Instrument [Line Items]
Total term debt	$ 500,000,000			$ 0
Debt instrument, maturity year	2019
Debt instrument, effective interest rate	1.39%	1.39%	1.39%	0.00%
Second quarter 2017 debt issuance of $10.0 billion | Floating-rate notes due 2020
Debt Instrument [Line Items]
Total term debt	$ 500,000,000			$ 0
Debt instrument, maturity year	2020
Debt instrument, effective interest rate	1.51%	1.51%	1.51%	0.00%
Second quarter 2017 debt issuance of $10.0 billion | Floating-rate notes due 2022
Debt Instrument [Line Items]
Total term debt	$ 1,000,000,000			$ 0
Debt instrument, maturity year	2022
Debt instrument, effective interest rate	1.81%	1.81%	1.81%	0.00%
Second quarter 2017 debt issuance of $10.0 billion | Fixed-rate 1.550% notes
Debt Instrument [Line Items]
Total term debt	$ 500,000,000			$ 0
Debt instrument, maturity year	2019
Debt instrument, stated interest rate	1.55%	1.55%	1.55%
Debt instrument, effective interest rate	1.59%	1.59%	1.59%	0.00%
Second quarter 2017 debt issuance of $10.0 billion | Fixed-rate 1.900% notes
Debt Instrument [Line Items]
Total term debt	$ 1,000,000,000			$ 0
Debt instrument, maturity year	2020
Debt instrument, stated interest rate	1.90%	1.90%	1.90%
Debt instrument, effective interest rate	1.51%	1.51%	1.51%	0.00%
Second quarter 2017 debt issuance of $10.0 billion | Fixed-rate 2.500% notes
Debt Instrument [Line Items]
Total term debt	$ 1,500,000,000			$ 0
Debt instrument, maturity year	2022
Debt instrument, stated interest rate	2.50%	2.50%	2.50%
Debt instrument, effective interest rate	1.80%	1.80%	1.80%	0.00%
Second quarter 2017 debt issuance of $10.0 billion | Fixed-rate 3.000% notes
Debt Instrument [Line Items]
Total term debt	$ 1,750,000,000			$ 0
Debt instrument, maturity year	2024
Debt instrument, stated interest rate	3.00%	3.00%	3.00%
Debt instrument, effective interest rate	2.11%	2.11%	2.11%	0.00%
Second quarter 2017 debt issuance of $10.0 billion | Fixed-rate 3.350% notes
Debt Instrument [Line Items]
Total term debt	$ 2,250,000,000			$ 0
Debt instrument, maturity year	2027
Debt instrument, stated interest rate	3.35%	3.35%	3.35%
Debt instrument, effective interest rate	2.25%	2.25%	2.25%	0.00%
Second quarter 2017 debt issuance of $10.0 billion | Fixed-rate 4.250% notes
Debt Instrument [Line Items]
Total term debt	$ 1,000,000,000			$ 0
Debt instrument, maturity year	2047
Debt instrument, stated interest rate	4.25%	4.25%	4.25%
Debt instrument, effective interest rate	4.26%	4.26%	4.26%	0.00%
Second quarter 2017 debt issuance of $1.0 billion
Debt Instrument [Line Items]
Debt instrument, face amount	$ 1,000,000,000
Second quarter 2017 debt issuance of $1.0 billion | Fixed-rate 4.300% notes
Debt Instrument [Line Items]
Total term debt	$ 1,000,000,000			$ 0
Debt instrument, maturity year	2047
Debt instrument, stated interest rate	4.30%	4.30%	4.30%
Debt instrument, effective interest rate	4.30%	4.30%	4.30%	0.00%
Third quarter 2017 debt issuance of $7.0 billion
Debt Instrument [Line Items]
Debt instrument, face amount	$ 7,000,000,000
Third quarter 2017 debt issuance of $7.0 billion | Floating-rate notes due 2020
Debt Instrument [Line Items]
Total term debt	$ 500,000,000			$ 0
Debt instrument, maturity year	2020
Debt instrument, effective interest rate	1.38%	1.38%	1.38%	0.00%
Third quarter 2017 debt issuance of $7.0 billion | Floating-rate notes due 2022
Debt Instrument [Line Items]
Total term debt	$ 750,000,000			$ 0
Debt instrument, maturity year	2022
Debt instrument, effective interest rate	1.66%	1.66%	1.66%	0.00%
Third quarter 2017 debt issuance of $7.0 billion | Fixed-rate 1.800% notes
Debt Instrument [Line Items]
Total term debt	$ 1,000,000,000			$ 0
Debt instrument, maturity year	2020
Debt instrument, stated interest rate	1.80%	1.80%	1.80%
Debt instrument, effective interest rate	1.84%	1.84%	1.84%	0.00%
Third quarter 2017 debt issuance of $7.0 billion | Fixed-rate 2.300% notes
Debt Instrument [Line Items]
Total term debt	$ 1,000,000,000			$ 0
Debt instrument, maturity year	2022
Debt instrument, stated interest rate	2.30%	2.30%	2.30%
Debt instrument, effective interest rate	2.34%	2.34%	2.34%	0.00%
Third quarter 2017 debt issuance of $7.0 billion | Fixed-rate 2.850% notes
Debt Instrument [Line Items]
Total term debt	$ 1,750,000,000			$ 0
Debt instrument, maturity year	2024
Debt instrument, stated interest rate	2.85%	2.85%	2.85%
Debt instrument, effective interest rate	2.25%	2.25%	2.25%	0.00%
Third quarter 2017 debt issuance of $7.0 billion | Fixed-rate 3.200% notes
Debt Instrument [Line Items]
Total term debt	$ 2,000,000,000			$ 0
Debt instrument, maturity year	2027
Debt instrument, stated interest rate	3.20%	3.20%	3.20%
Debt instrument, effective interest rate	2.43%	2.43%	2.43%	0.00%
Third quarter 2017 euro-denominated debt issuance
Debt Instrument [Line Items]
Debt instrument, face amount | €			€ 2,500,000,000.0
Third quarter 2017 euro-denominated debt issuance | Fixed-rate 0.875% notes
Debt Instrument [Line Items]
Total term debt	$ 1,469,000,000			$ 0
Debt instrument, maturity year	2025
Debt instrument, stated interest rate	0.875%	0.875%	0.875%
Debt instrument, effective interest rate	3.03%	3.03%	3.03%	0.00%
Third quarter 2017 euro-denominated debt issuance | Fixed-rate 1.375% notes
Debt Instrument [Line Items]
Total term debt	$ 1,469,000,000			$ 0
Debt instrument, maturity year	2029
Debt instrument, stated interest rate	1.375%	1.375%	1.375%
Debt instrument, effective interest rate	3.37%	3.37%	3.37%	0.00%
Third quarter 2017 debt issuance of $1.0 billion
Debt Instrument [Line Items]
Debt instrument, face amount	$ 1,000,000,000
Third quarter 2017 debt issuance of $1.0 billion | Fixed-rate 3.000% notes
Debt Instrument [Line Items]
Total term debt	$ 1,000,000,000			$ 0
Debt instrument, maturity year	2027
Debt instrument, stated interest rate	3.00%	3.00%	3.00%
Debt instrument, effective interest rate	3.03%	3.03%	3.03%	0.00%
Fourth quarter 2017 Canadian dollar-denominated debt issuance
Debt Instrument [Line Items]
Debt instrument, face amount | CAD		CAD 2,500,000,000.0
Fourth quarter 2017 Canadian dollar-denominated debt issuance | Fixed-rate 2.513% notes
Debt Instrument [Line Items]
Total term debt	$ 2,017,000,000			$ 0
Debt instrument, maturity year	2024
Debt instrument, stated interest rate	2.513%	2.513%	2.513%
Debt instrument, effective interest rate	2.66%	2.66%	2.66%	0.00%
Fourth quarter 2017 debt issuance of $5.0 billion
Debt Instrument [Line Items]
Debt instrument, face amount	$ 5,000,000,000
Fourth quarter 2017 debt issuance of $5.0 billion | Fixed-rate 1.500% notes
Debt Instrument [Line Items]
Total term debt	$ 1,000,000,000			$ 0
Debt instrument, maturity year	2019
Debt instrument, stated interest rate	1.50%	1.50%	1.50%
Debt instrument, effective interest rate	1.54%	1.54%	1.54%	0.00%
Fourth quarter 2017 debt issuance of $5.0 billion | Fixed-rate 2.100% notes
Debt Instrument [Line Items]
Total term debt	$ 1,000,000,000			$ 0
Debt instrument, maturity year	2022
Debt instrument, stated interest rate	2.10%	2.10%	2.10%
Debt instrument, effective interest rate	1.92%	1.92%	1.92%	0.00%
Fourth quarter 2017 debt issuance of $5.0 billion | Fixed-rate 2.900% notes
Debt Instrument [Line Items]
Total term debt	$ 2,000,000,000			$ 0
Debt instrument, maturity year	2027
Debt instrument, stated interest rate	2.90%	2.90%	2.90%
Debt instrument, effective interest rate	2.55%	2.55%	2.55%	0.00%
Fourth quarter 2017 debt issuance of $5.0 billion | Fixed-rate 3.750% notes
Debt Instrument [Line Items]
Total term debt	$ 1,000,000,000			$ 0
Debt instrument, maturity year	2047
Debt instrument, stated interest rate	3.75%	3.75%	3.75%
Debt instrument, effective interest rate	3.78%	3.78%	3.78%	0.00%