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

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Debt - Extinguishments of Debt (Details) € in Millions, $ in Millions	3 Months Ended					12 Months Ended
	Sep. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2021 EUR (€)
Extinguishment of Debt [Line Items]
Long-Term Debt	$ 17,110			$ 17,224		$ 17,110	$ 17,224
Debt Instrument, Repurchase Amount				951			951
Losses on debt extinguishment				(1)		(178)	(8)	$ (59)
Long-term Debt
Extinguishment of Debt [Line Items]
Long-Term Debt				950			950
Notes 2.894% due June 6, 2022
Extinguishment of Debt [Line Items]
Debt Instrument, Repurchased Face Amount	$ 1,535		$ 265			$ 1,535
Interest rate	2.894%					2.894%
Debt Instrument, Repurchase Amount	$ 1,566		275			$ 1,566
Losses on debt extinguishment	(32)		(10)
Notes 2.894% due June 6, 2022 \| Long-term Debt
Extinguishment of Debt [Line Items]
Long-Term Debt	1,534		$ 265			1,534
3.300% Notes due March 1, 2023
Extinguishment of Debt [Line Items]
Debt Instrument, Repurchased Face Amount	$ 294					$ 294
Interest rate	3.30%					3.30%
Long-Term Debt	$ 0			295		$ 0	295
Debt Instrument, Repurchase Amount	307					307
Losses on debt extinguishment	(12)
3.300% Notes due March 1, 2023 \| Long-term Debt
Extinguishment of Debt [Line Items]
Long-Term Debt	295					295
Notes 3.875% due May 15, 2024
Extinguishment of Debt [Line Items]
Debt Instrument, Repurchased Face Amount	33					33
Debt Instrument, Repurchase Amount	35					35
Losses on debt extinguishment	(2)
Notes 3.875% due May 15, 2024 \| Long-term Debt
Extinguishment of Debt [Line Items]
Long-Term Debt	33					33
3.734% Notes due December 15, 2024
Extinguishment of Debt [Line Items]
Debt Instrument, Repurchased Face Amount	$ 500					$ 500
Interest rate	3.734%					3.734%
Long-Term Debt	$ 873			1,370		$ 873	1,370
Debt Instrument, Repurchase Amount	546					546
Losses on debt extinguishment	(48)
3.734% Notes due December 15, 2024 \| Long-term Debt
Extinguishment of Debt [Line Items]
Long-Term Debt	499					499
3.363% Notes due June 6, 2024
Extinguishment of Debt [Line Items]
Debt Instrument, Repurchased Face Amount	$ 752					$ 752
Interest rate	3.363%					3.363%
Long-Term Debt	$ 994			1,742		$ 994	1,742
Debt Instrument, Repurchase Amount	808					808
Losses on debt extinguishment	(58)
3.363% Notes due June 6, 2024 \| Long-term Debt
Extinguishment of Debt [Line Items]
Long-Term Debt	$ 750					$ 750
Notes 3.125% due November 8, 2021
Extinguishment of Debt [Line Items]
Debt Instrument, Repurchased Face Amount		$ 1,000
Interest rate	3.125%					3.125%
Debt Instrument, Repurchase Amount		1,019
Losses on debt extinguishment		(14)
Notes 3.125% due November 8, 2021 \| Long-term Debt
Extinguishment of Debt [Line Items]
Long-Term Debt		1,005
Notes 0.174% due June 4, 2021 [Member]
Extinguishment of Debt [Line Items]
Interest rate	0.174%					0.174%
Debt Instrument, Repurchase Amount		730
Losses on debt extinguishment		(1)
Notes 0.174% due June 4, 2021 [Member] \| Long-term Debt
Extinguishment of Debt [Line Items]
Long-Term Debt		728
Notes 0.174% due June 4, 2021 [Member] \| Euro Member Countries, Euro
Extinguishment of Debt [Line Items]
Debt Instrument, Repurchased Face Amount \| €									€ 600
Notes 0.174% due June 4, 2021 [Member] \| United States of America, Dollars
Extinguishment of Debt [Line Items]
Debt Instrument, Repurchased Face Amount		$ 728
Notes 2.404% due June 5, 2020 [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Repurchased Face Amount					$ 1,000
Interest rate	2.404%					2.404%
Losses on debt extinguishment					0
Notes 2.404% due June 5, 2020 [Member] \| Long-term Debt
Extinguishment of Debt [Line Items]
Long-Term Debt					1,000
Notes 3.250% due November 12, 2020 [Member]
Extinguishment of Debt [Line Items]
Debt Instrument, Repurchased Face Amount				200	500		200
Interest rate	3.25%					3.25%
Debt Instrument, Repurchase Amount					506
Losses on debt extinguishment					(6)
Notes 3.250% due November 12, 2020 [Member] \| Long-term Debt
Extinguishment of Debt [Line Items]
Long-Term Debt					$ 500
Floating Rate Notes Due December 29, 2020
Extinguishment of Debt [Line Items]
Debt Instrument, Repurchased Face Amount				$ 750			$ 750