Debt - Debt (Details) - USD ($) $ in Millions	Mar. 31, 2017	Sep. 30, 2016
Debt Instrument [Line Items]
Principal Amount, current	$ 1,750	$ 0
Unamortized Discounts and Debt Issuance Costs, current	(2)	0
Carrying Amount, current	1,748	0
Principal Amount, noncurrent	14,250	16,000
Unamortized Discounts and Debt Issuance Costs, noncurrent	(110)	(118)
Carrying Amount, noncurrent	14,140	15,882
Total debt, principal	16,000	16,000
Unamortized Discounts and Debt Issuance Costs	(112)	(118)
Carrying Amount	$ 15,888	15,882
Senior Notes \| 2017 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	1.20%
Principal Amount, current	$ 1,750	0
Unamortized Discounts and Debt Issuance Costs, current	(2)	0
Carrying Amount, current	1,748	0
Principal Amount, noncurrent	0	1,750
Unamortized Discounts and Debt Issuance Costs, noncurrent	0	(4)
Carrying Amount, noncurrent	$ 0	1,746
Effective Interest Rate (percent)	1.37%
Senior Notes \| 2020 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	2.20%
Principal Amount, noncurrent	$ 3,000	3,000
Unamortized Discounts and Debt Issuance Costs, noncurrent	(11)	(12)
Carrying Amount, noncurrent	$ 2,989	2,988
Effective Interest Rate (percent)	2.30%
Senior Notes \| 2022 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	2.80%
Principal Amount, noncurrent	$ 2,250	2,250
Unamortized Discounts and Debt Issuance Costs, noncurrent	(11)	(12)
Carrying Amount, noncurrent	$ 2,239	2,238
Effective Interest Rate (percent)	2.89%
Senior Notes \| 2025 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	3.15%
Principal Amount, noncurrent	$ 4,000	4,000
Unamortized Discounts and Debt Issuance Costs, noncurrent	(34)	(36)
Carrying Amount, noncurrent	$ 3,966	3,964
Effective Interest Rate (percent)	3.26%
Senior Notes \| 2035 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	4.15%
Principal Amount, noncurrent	$ 1,500	1,500
Unamortized Discounts and Debt Issuance Costs, noncurrent	(15)	(15)
Carrying Amount, noncurrent	$ 1,485	1,485
Effective Interest Rate (percent)	4.23%
Senior Notes \| 2045 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	4.30%
Principal Amount, noncurrent	$ 3,500	3,500
Unamortized Discounts and Debt Issuance Costs, noncurrent	(39)	(39)
Carrying Amount, noncurrent	$ 3,461	$ 3,461
Effective Interest Rate (percent)	4.37%

Amount of short-term debt and current maturity of long-term debt and capital lease obligations due within one year or the normal operating cycle, if longer.

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

+ Details

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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Represents the aggregate of total long-term debt, including current maturities and short-term debt.

+ References

No definition available.

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- Definition

Amount, after accumulated amortization, of debt issuance costs classified as current. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

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-Name Accounting Standards Codification
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Amount, after accumulated amortization, of debt issuance costs classified as noncurrent. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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- Definition

Debt, Long-term and Short-term, Gross

+ References

No definition available.

+ Details

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