Debt - Senior Notes (Details) - USD ($) $ in Millions	Mar. 31, 2016	Sep. 30, 2015
Debt Instrument [Line Items]
Principal Amount	$ 16,000
Unamortized discounts and Debt Issuance Costs	(124)
Long-term Debt	$ 15,876	$ 0
Senior Notes \| 2017 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	1.20%
Principal Amount	$ 1,750
Unamortized discounts and Debt Issuance Costs	(5)
Long-term Debt	$ 1,745
Effective Interest Rate (percent)	1.37%
Senior Notes \| 2020 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	2.20%
Principal Amount	$ 3,000
Unamortized discounts and Debt Issuance Costs	(14)
Long-term Debt	$ 2,986
Effective Interest Rate (percent)	2.30%
Senior Notes \| 2022 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	2.80%
Principal Amount	$ 2,250
Unamortized discounts and Debt Issuance Costs	(13)
Long-term Debt	$ 2,237
Effective Interest Rate (percent)	2.89%
Senior Notes \| 2025 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	3.15%
Principal Amount	$ 4,000
Unamortized discounts and Debt Issuance Costs	(38)
Long-term Debt	$ 3,962
Effective Interest Rate (percent)	3.26%
Senior Notes \| 2035 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	4.15%
Principal Amount	$ 1,500
Unamortized discounts and Debt Issuance Costs	(15)
Long-term Debt	$ 1,485
Effective Interest Rate (percent)	4.23%
Senior Notes \| 2045 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	4.30%
Principal Amount	$ 3,500
Unamortized discounts and Debt Issuance Costs	(39)
Long-term Debt	$ 3,461
Effective Interest Rate (percent)	4.37%

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

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)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
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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

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

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No definition available.

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- Definition

The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 30
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- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 210
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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