Fair Value Measurements and Investments Carrying amount and estimated fair value of debt (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Debt Instrument [Line Items]
Carrying amount of current maturities of long-term debt	$ 1,749	$ 0
Carrying Amount	16,618	15,882
Senior Notes
Debt Instrument [Line Items]
Carrying amount of current maturities of long-term debt	1,749
Carrying Amount	16,618	15,882
Debt, Long-term and Short-term, Combined Amount	$ 18,367	15,882
2017 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	1.20%
2017 Notes \| Senior Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	1.20%
Carrying amount of current maturities of long-term debt	$ 1,749
Carrying Amount		1,746
2020 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	2.20%
2020 Notes \| Senior Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	2.20%
Carrying Amount	$ 2,990	2,988
September 2022 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	2.15%
September 2022 Notes \| Senior Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	2.15%
Carrying Amount	$ 993	0
2022 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	2.80%
2022 Notes \| Senior Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	2.80%
Carrying Amount	$ 2,240	2,238
2025 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	3.15%
2025 Notes \| Senior Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	3.15%
Carrying Amount	$ 3,967	3,964
2027 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	2.75%
2027 Notes \| Senior Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	2.75%
Carrying Amount	$ 740	0
2035 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	4.15%
2035 Notes \| Senior Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	4.15%
Carrying Amount	$ 1,485	1,485
2045 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	4.30%
2045 Notes \| Senior Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	4.30%
Carrying Amount	$ 3,463	3,461
2047 Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	3.65%
2047 Notes \| Senior Notes
Debt Instrument [Line Items]
Stated interest rate (percent)	3.65%
Carrying Amount	$ 740	0
Estimate of Fair Value Measurement \| Senior Notes
Debt Instrument [Line Items]
Estimated Fair Value	19,171	17,158
Estimate of Fair Value Measurement \| 2017 Notes \| Senior Notes
Debt Instrument [Line Items]
Estimated Fair Value	1,751	1,754
Estimate of Fair Value Measurement \| 2020 Notes \| Senior Notes
Debt Instrument [Line Items]
Estimated Fair Value	3,031	3,077
Estimate of Fair Value Measurement \| September 2022 Notes \| Senior Notes
Debt Instrument [Line Items]
Estimated Fair Value	997	0
Estimate of Fair Value Measurement \| 2022 Notes \| Senior Notes
Debt Instrument [Line Items]
Estimated Fair Value	2,301	2,359
Estimate of Fair Value Measurement \| 2025 Notes \| Senior Notes
Debt Instrument [Line Items]
Estimated Fair Value	4,098	4,225
Estimate of Fair Value Measurement \| 2027 Notes \| Senior Notes
Debt Instrument [Line Items]
Estimated Fair Value	737	0
Estimate of Fair Value Measurement \| 2035 Notes \| Senior Notes
Debt Instrument [Line Items]
Estimated Fair Value	1,637	1,698
Estimate of Fair Value Measurement \| 2045 Notes \| Senior Notes
Debt Instrument [Line Items]
Estimated Fair Value	3,873	4,045
Estimate of Fair Value Measurement \| 2047 Notes \| Senior Notes
Debt Instrument [Line Items]
Estimated Fair Value	$ 746	$ 0

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

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(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: 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

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+ 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 210.5-02.19,20)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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