Borrowings - Narrative (Details)			1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 22, 2020 USD ($)	May 29, 2020 USD ($)	Jun. 30, 2020 USD ($)	Jul. 31, 2020 USD ($) commercial_paper_program	Jul. 31, 2019 USD ($)	Jul. 31, 2020 USD ($) commercial_paper_program	Jul. 31, 2019 USD ($)	Mar. 31, 2020 USD ($)	Oct. 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Issuance costs			$ 26,000,000	$ 38,000,000		$ 38,000,000			$ 16,000,000
Notional amount				20,861,000,000		20,861,000,000			$ 23,669,000,000
Loss on extinguishment of debt				$ 40,000,000	$ 0	$ 40,000,000	$ 0
Number of commercial paper programs | commercial_paper_program				2		2
Treasury Lock | Cash flow hedges
Line of Credit Facility [Line Items]
Notional amount				$ 750,000,000		$ 750,000,000		$ 750,000,000
Interest Rate Swap
Line of Credit Facility [Line Items]
Notional amount			500,000,000	500,000,000		500,000,000
Shelf Registration 2019
Line of Credit Facility [Line Items]
Face amount of debt instrument			3,000,000,000.0
$1,150 issued at discount to par at a price of 99.769% in June 2020 at 2.2%, due June 2025
Line of Credit Facility [Line Items]
Face amount of debt instrument			$ 1,150,000,000	$ 1,150,000,000		$ 1,150,000,000
Interest rate (percent)			2.20%	2.20%		2.20%
$1,000 issued at discount to par at a price of 99.718% in June 2020 at 3.0%, due June 2027
Line of Credit Facility [Line Items]
Face amount of debt instrument			$ 1,000,000,000.0	$ 1,000,000,000		$ 1,000,000,000
Interest rate (percent)			3.00%	3.00%		3.00%
$850 issued at discount to par at a price of 99.790% in June 2020 at 3.4%, due June 2030
Line of Credit Facility [Line Items]
Face amount of debt instrument			$ 850,000,000	$ 850,000,000		$ 850,000,000
Interest rate (percent)			3.40%	3.40%		3.40%
$1,350 issued at discount to par at a price of 99.827% in December 2010 at 3.75%, due December 2020
Line of Credit Facility [Line Items]
Face amount of debt instrument				$ 1,350,000,000		$ 1,350,000,000
Interest rate (percent)	3.75%		3.75%	3.75%		3.75%
Repurchased amount	$ 500,000,000
$1,250 issued at discount to par at a price of 99.799% in May 2011 at 4.3%, due June 2021
Line of Credit Facility [Line Items]
Face amount of debt instrument				$ 1,250,000,000		$ 1,250,000,000
Interest rate (percent)	4.30%		4.30%	4.30%		4.30%
Repurchased amount	$ 400,000,000
$1,000 issued at discount to par at a price of 99.816% in September 2011 at 4.375%, due September 2021
Line of Credit Facility [Line Items]
Face amount of debt instrument				$ 1,000,000,000		$ 1,000,000,000
Interest rate (percent)			4.375%	4.375%		4.375%
$1,500 issued at discount to par at a price of 99.707% in December 2011 at 4.65%, due December 2021
Line of Credit Facility [Line Items]
Face amount of debt instrument				$ 1,500,000,000		$ 1,500,000,000
Interest rate (percent)			4.65%	4.65%		4.65%
Shelf Registration 2009, Due December 2020, June 2021, September 2021, And December 2021
Line of Credit Facility [Line Items]
Repurchased amount			$ 700,000,000
Loss on extinguishment of debt			23,000,000
Shelf Registration Due December 2020 and September 2021
Line of Credit Facility [Line Items]
Repurchased amount			$ 900,000,000
Loss on extinguishment of debt	$ 17,000,000
Commercial paper
Line of Credit Facility [Line Items]
Maximum borrowing capacity under credit facility				$ 6,000,000,000.0		$ 6,000,000,000.0
Revolving credit facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity under credit facility				4,000,000,000.0		4,000,000,000.0
Senior unsecured revolving credit facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity under credit facility		$ 1,000,000,000.0
Revolving credit facility, term		364 days
Credit facilities
Line of Credit Facility [Line Items]
Available borrowing resources				$ 725,000,000		$ 725,000,000