Long-Term Debt (Detail) - USD ($)	Sep. 30, 2020	Aug. 31, 2020	Jun. 30, 2020	Apr. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Credit Facility	$ 900,000,000				$ 0
Finance lease obligations	153,000,000				157,000,000
Total debt	10,995,000,000				10,940,000,000
Less current portion	(1,316,000,000)				(977,000,000)
Long-term debt, noncurrent	9,679,000,000				9,963,000,000
Series L Notes, interest rate of 3.3%, face amount of $173, maturing September 15, 2022 (effective interest rate of 3.4%)
Debt Instrument [Line Items]
Senior notes	173,000,000				349,000,000
Series M Notes, interest rate of 3.4%, face amount of $350, matured October 15, 2020 (effective interest rate of 3.6%)
Debt Instrument [Line Items]
Senior notes	0				349,000,000
Series N Notes, interest rate of 3.1%, face amount of $400, maturing October 15, 2021 (effective interest rate of 3.4%)
Debt Instrument [Line Items]
Senior notes	399,000,000				398,000,000
Series O Notes, interest rate of 2.9%, face amount of $450, maturing March 1, 2021 (effective interest rate of 3.1%)
Debt Instrument [Line Items]
Senior notes	450,000,000				449,000,000
Series P Notes, interest rate of 3.8%, face amount of $350, maturing October 1, 2025 (effective interest rate of 4.0%)
Debt Instrument [Line Items]
Senior notes	346,000,000				346,000,000
Series Q Notes, interest rate of 2.3%, face amount of $399, maturing January 15, 2022 (effective interest rate of 2.5%)
Debt Instrument [Line Items]
Senior notes	398,000,000				747,000,000
Series R Notes, interest rate of 3.1%, face amount of $750, maturing June 15, 2026 (effective interest rate of 3.3%)
Debt Instrument [Line Items]
Senior notes	745,000,000				744,000,000
Series U Notes, interest rate of 3.1%, face amount of $291, maturing February 15, 2023 (effective interest rate of 3.1%)
Debt Instrument [Line Items]
Senior notes	291,000,000				291,000,000
Series V Notes, interest rate of 3.8%, face amount of $318, maturing March 15, 2025 (effective interest rate of 2.8%)
Debt Instrument [Line Items]
Senior notes	330,000,000				332,000,000
Series W Notes, interest rate of 4.5%, face amount of $278, maturing October 1, 2034 (effective interest rate of 4.1%)
Debt Instrument [Line Items]
Senior notes	291,000,000				291,000,000
Series X Notes, interest rate of 4.0%, face amount of $450, maturing April 15, 2028 (effective interest rate of 4.2%)
Debt Instrument [Line Items]
Senior notes	444,000,000				444,000,000
Series Y Notes, floating rate, face amount of $550, maturing December 1, 2020 (effective interest rate of 0.8% at September 30, 2020)
Debt Instrument [Line Items]
Senior notes	550,000,000				549,000,000
Series Z Notes, interest rate of 4.2%, face amount of $350, maturing December 1, 2023 (effective interest rate of 4.4%)
Debt Instrument [Line Items]
Senior notes	348,000,000				347,000,000
Series AA Notes, interest rate of 4.7%, face amount of $300, maturing December 1, 2028 (effective interest rate of 4.8%)
Debt Instrument [Line Items]
Senior notes	297,000,000				297,000,000
Series BB Notes, floating rate, face amount of $300, maturing March 8, 2021 (effective interest rate of 0.9% at September 30, 2020)
Debt Instrument [Line Items]
Senior notes	300,000,000				299,000,000
Series CC Notes, interest rate of 3.6%, face amount of $550, maturing April 15, 2024 (effective interest rate of 3.9%)
Debt Instrument [Line Items]
Senior notes	590,000,000				564,000,000
Series DD Notes, interest rate of 2.1%, face amount of $224, maturing October 3, 2022 (effective interest rate of 1.2%)
Debt Instrument [Line Items]
Senior notes	229,000,000				543,000,000
Series EE Notes, interest rate of 5.8%, face amount of $1,600, maturing May 1, 2025 (effective interest rate of 6.0%)
Debt Instrument [Line Items]
Senior notes	1,582,000,000				0
Series FF Notes, interest rate of 4.6%, face amount of $1,000, maturing June 15, 2030 (effective interest rate of 4.8%)
Debt Instrument [Line Items]
Senior notes	985,000,000				0
Series GG Notes, interest rate of 3.5%, face amount of $1,000, maturing October 15, 2032 (effective interest rate of 3.7%)
Debt Instrument [Line Items]
Senior notes	$ 984,000,000				0
Senior Notes | Series L Notes, interest rate of 3.3%, face amount of $173, maturing September 15, 2022 (effective interest rate of 3.4%)
Debt Instrument [Line Items]
Interest rate	3.30%		3.30%
Senior notes, face amount	$ 173,000,000
Effective interest rate	3.40%
Senior Notes | Series M Notes, interest rate of 3.4%, face amount of $350, matured October 15, 2020 (effective interest rate of 3.6%)
Debt Instrument [Line Items]
Interest rate	3.40%
Senior notes, face amount	$ 350,000,000
Effective interest rate	3.60%
Senior Notes | Series N Notes, interest rate of 3.1%, face amount of $400, maturing October 15, 2021 (effective interest rate of 3.4%)
Debt Instrument [Line Items]
Interest rate	3.10%
Senior notes, face amount	$ 400,000,000
Effective interest rate	3.40%
Senior Notes | Series O Notes, interest rate of 2.9%, face amount of $450, maturing March 1, 2021 (effective interest rate of 3.1%)
Debt Instrument [Line Items]
Interest rate	2.90%
Senior notes, face amount	$ 450,000,000
Effective interest rate	3.10%
Senior Notes | Series P Notes, interest rate of 3.8%, face amount of $350, maturing October 1, 2025 (effective interest rate of 4.0%)
Debt Instrument [Line Items]
Interest rate	3.80%
Senior notes, face amount	$ 350,000,000
Effective interest rate	4.00%
Senior Notes | Series Q Notes, interest rate of 2.3%, face amount of $399, maturing January 15, 2022 (effective interest rate of 2.5%)
Debt Instrument [Line Items]
Interest rate	2.30%		2.30%
Senior notes, face amount	$ 399,000,000
Effective interest rate	2.50%
Senior Notes | Series R Notes, interest rate of 3.1%, face amount of $750, maturing June 15, 2026 (effective interest rate of 3.3%)
Debt Instrument [Line Items]
Interest rate	3.10%
Senior notes, face amount	$ 750,000,000
Effective interest rate	3.30%
Senior Notes | Series U Notes, interest rate of 3.1%, face amount of $291, maturing February 15, 2023 (effective interest rate of 3.1%)
Debt Instrument [Line Items]
Interest rate	3.10%
Senior notes, face amount	$ 291,000,000
Effective interest rate	3.10%
Senior Notes | Series V Notes, interest rate of 3.8%, face amount of $318, maturing March 15, 2025 (effective interest rate of 2.8%)
Debt Instrument [Line Items]
Interest rate	3.80%
Senior notes, face amount	$ 318,000,000
Effective interest rate	2.80%
Senior Notes | Series W Notes, interest rate of 4.5%, face amount of $278, maturing October 1, 2034 (effective interest rate of 4.1%)
Debt Instrument [Line Items]
Interest rate	4.50%
Senior notes, face amount	$ 278,000,000
Effective interest rate	4.10%
Senior Notes | Series X Notes, interest rate of 4.0%, face amount of $450, maturing April 15, 2028 (effective interest rate of 4.2%)
Debt Instrument [Line Items]
Interest rate	4.00%
Senior notes, face amount	$ 450,000,000
Effective interest rate	4.20%
Senior Notes | Series Y Notes, floating rate, face amount of $550, maturing December 1, 2020 (effective interest rate of 0.8% at September 30, 2020)
Debt Instrument [Line Items]
Senior notes, face amount	$ 550,000,000
Effective interest rate	0.80%
Senior Notes | Series Z Notes, interest rate of 4.2%, face amount of $350, maturing December 1, 2023 (effective interest rate of 4.4%)
Debt Instrument [Line Items]
Interest rate	4.20%
Senior notes, face amount	$ 350,000,000
Effective interest rate	4.40%
Senior Notes | Series AA Notes, interest rate of 4.7%, face amount of $300, maturing December 1, 2028 (effective interest rate of 4.8%)
Debt Instrument [Line Items]
Interest rate	4.70%
Senior notes, face amount	$ 300,000,000
Effective interest rate	4.80%
Senior Notes | Series BB Notes, floating rate, face amount of $300, maturing March 8, 2021 (effective interest rate of 0.9% at September 30, 2020)
Debt Instrument [Line Items]
Senior notes, face amount	$ 300,000,000
Effective interest rate	0.90%
Senior Notes | Series CC Notes, interest rate of 3.6%, face amount of $550, maturing April 15, 2024 (effective interest rate of 3.9%)
Debt Instrument [Line Items]
Interest rate	3.60%
Senior notes, face amount	$ 550,000,000
Effective interest rate	3.90%
Senior Notes | Series DD Notes, interest rate of 2.1%, face amount of $224, maturing October 3, 2022 (effective interest rate of 1.2%)
Debt Instrument [Line Items]
Interest rate	2.10%		2.10%
Senior notes, face amount	$ 224,000,000
Effective interest rate	1.20%
Senior Notes | Series EE Notes, interest rate of 5.8%, face amount of $1,600, maturing May 1, 2025 (effective interest rate of 6.0%)
Debt Instrument [Line Items]
Interest rate	5.80%			5.75%
Senior notes, face amount	$ 1,600,000,000			$ 1,600,000,000
Effective interest rate	6.00%
Senior Notes | Series FF Notes, interest rate of 4.6%, face amount of $1,000, maturing June 15, 2030 (effective interest rate of 4.8%)
Debt Instrument [Line Items]
Interest rate	4.60%		4.625%
Senior notes, face amount	$ 1,000,000,000		$ 1,000,000,000.0
Effective interest rate	4.80%
Senior Notes | Series GG Notes, interest rate of 3.5%, face amount of $1,000, maturing October 15, 2032 (effective interest rate of 3.7%)
Debt Instrument [Line Items]
Interest rate	3.50%	3.50%
Senior notes, face amount	$ 1,000,000,000	$ 1,000,000,000.0
Effective interest rate	3.70%
Commercial paper
Debt Instrument [Line Items]
Commercial paper	$ 30,000,000				3,197,000,000
Other
Debt Instrument [Line Items]
Other	$ 180,000,000				$ 247,000,000