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Long-Term Debt (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Credit Facility	$ 0		$ 0
Finance lease obligations	160		163
Total debt	10,414		9,347
Less: Current portion of long-term debt	(229)		(833)
Long-term debt, noncurrent	10,185		8,514
Series K Notes, interest rate of 3.0%, face amount of $600, matured March 1, 2019 (effective interest rate of 4.4%)
Debt Instrument [Line Items]
Senior notes	0		600
Series L Notes, interest rate of 3.3%, face amount of $350, maturing September 15, 2022 (effective interest rate of 3.4%)
Debt Instrument [Line Items]
Senior notes	349		349
Series M Notes, interest rate of 3.4%, face amount of $350, maturing October 15, 2020 (effective interest rate of 3.6%)
Debt Instrument [Line Items]
Senior notes	349		349
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	398		397
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	449		448
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	345		345
Series Q Notes, interest rate of 2.3%, face amount of $750, maturing January 15, 2022 (effective interest rate of 2.5%)
Debt Instrument [Line Items]
Senior notes	746		745
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	744		743
Series T Notes, interest rate of 7.2%, face amount of $181, maturing December 1, 2019 (effective interest rate of 2.3%)
Debt Instrument [Line Items]
Senior notes	184		188
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		291
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	334		335
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		292
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		443
Series Y Notes, floating rate, face amount of $550, maturing December 1, 2020 (effective interest rate of 3.1% at June 30, 2019)
Debt Instrument [Line Items]
Senior notes	548		547
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	347		347
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		297
Series BB Notes, floating rate, face amount of $300, maturing March 8, 2021 (effective interest rate of 3.1% at June 30, 2019)
Debt Instrument [Line Items]
Senior notes	299		0
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	$ 564		0
Senior Notes \| Series K Notes, interest rate of 3.0%, face amount of $600, matured March 1, 2019 (effective interest rate of 4.4%)
Debt Instrument [Line Items]
Interest rate	3.00%
Senior notes, face amount	$ 600
Effective interest rate	4.40%
Senior Notes \| Series L Notes, interest rate of 3.3%, face amount of $350, maturing September 15, 2022 (effective interest rate of 3.4%)
Debt Instrument [Line Items]
Interest rate	3.30%
Senior notes, face amount	$ 350
Effective interest rate	3.40%
Senior Notes \| Series M Notes, interest rate of 3.4%, face amount of $350, maturing October 15, 2020 (effective interest rate of 3.6%)
Debt Instrument [Line Items]
Interest rate	3.40%
Senior notes, face amount	$ 350
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
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
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
Effective interest rate	4.00%
Senior Notes \| Series Q Notes, interest rate of 2.3%, face amount of $750, maturing January 15, 2022 (effective interest rate of 2.5%)
Debt Instrument [Line Items]
Interest rate	2.30%
Senior notes, face amount	$ 750
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
Effective interest rate	3.30%
Senior Notes \| Series T Notes, interest rate of 7.2%, face amount of $181, maturing December 1, 2019 (effective interest rate of 2.3%)
Debt Instrument [Line Items]
Interest rate	7.20%
Senior notes, face amount	$ 181
Effective interest rate	2.30%
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
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
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
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
Effective interest rate	4.20%
Senior Notes \| Series Y Notes, floating rate, face amount of $550, maturing December 1, 2020 (effective interest rate of 3.1% at June 30, 2019)
Debt Instrument [Line Items]
Senior notes, face amount	$ 550
Effective interest rate	3.10%
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
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
Effective interest rate	4.80%
Senior Notes \| Series BB Notes, floating rate, face amount of $300, maturing March 8, 2021 (effective interest rate of 3.1% at June 30, 2019)
Debt Instrument [Line Items]
Senior notes, face amount	$ 300	$ 300
Effective interest rate	3.10%
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%	3.60%
Senior notes, face amount	$ 550	$ 550
Effective interest rate	3.90%
Commercial paper
Debt Instrument [Line Items]
Commercial paper	$ 3,069		2,245
Other
Debt Instrument [Line Items]
Other	$ 206		$ 223