Long-Term Debt (Detail) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Credit Facility	$ 400,000,000	$ 900,000,000
Finance lease obligations	151,000,000	153,000,000
Total debt	10,208,000,000	10,376,000,000
Less current portion	(822,000,000)	(1,173,000,000)
Long-term debt, noncurrent	9,386,000,000	9,203,000,000
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	173,000,000
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	400,000,000	399,000,000
Series O Notes, interest rate of 2.9%, face amount of $450, matured March 1, 2021 (effective interest rate of 3.1%)
Debt Instrument [Line Items]
Senior notes	0	450,000,000
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	347,000,000	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	398,000,000
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	745,000,000
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	329,000,000	330,000,000
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	290,000,000	290,000,000
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	445,000,000	445,000,000
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	348,000,000
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, matured March 8, 2021
Debt Instrument [Line Items]
Senior notes	0	300,000,000
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	579,000,000	586,000,000
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	228,000,000	228,000,000
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	1,584,000,000	1,583,000,000
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	986,000,000	986,000,000
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	985,000,000	985,000,000
Series HH Notes, interest rate of 2.9%, face amount of $1,100, maturing April 15, 2031 (effective interest rate of 3.0%)
Debt Instrument [Line Items]
Senior notes	$ 1,089,000,000	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%
Senior notes, face amount	$ 173,000,000
Effective interest rate	3.40%
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, matured 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%
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 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, matured March 8, 2021
Debt Instrument [Line Items]
Senior notes, face amount	$ 300,000,000
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%
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%
Senior notes, face amount	$ 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%
Senior notes, face amount	$ 1,000,000,000
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%
Senior notes, face amount	$ 1,000,000,000
Effective interest rate	3.70%
Senior Notes | Series HH Notes, interest rate of 2.9%, face amount of $1,100, maturing April 15, 2031 (effective interest rate of 3.0%)
Debt Instrument [Line Items]
Interest rate	2.85%
Senior notes, face amount	$ 1,100,000,000
Effective interest rate	3.00%
Commercial paper
Debt Instrument [Line Items]
Commercial paper	$ 0	0
Other
Debt Instrument [Line Items]
Other	$ 143,000,000	$ 143,000,000