Debt - Additional Information (Detail) - USD ($)	1 Months Ended	6 Months Ended	12 Months Ended
	Oct. 31, 2017	Dec. 31, 2017	Jun. 30, 2017
Debt Instrument [Line Items]
Commercial paper		$ 12,500,000,000	$ 9,100,000,000
Credit facility, financial covenant		As of December 31, 2017, we were in compliance with the only financial covenant in both credit agreements, which requires us to maintain a coverage ratio of at least three times earnings before interest, taxes, depreciation, and amortization to interest expense, as defined in the credit agreements.
Credit facility, drawn		$ 0	0
Long-term debt		76,800,000,000	77,100,000,000
Long-term debt fair value		81,700,000,000	80,300,000,000
Debt issuance costs and unamortized discount		$ 688,000,000	$ 715,000,000
Credit Facility Expire on October 30th 2018
Debt Instrument [Line Items]
Credit facility	$ 5,000,000,000
Credit facility, expiration date	Oct. 30, 2018
Credit Facility Expire on October 31st 2022
Debt Instrument [Line Items]
Credit facility	$ 5,000,000,000
Credit facility, expiration date	Oct. 31, 2022
Commercial paper
Debt Instrument [Line Items]
Commercial paper, weighted average interest rate		1.31%	1.01%
Commercial paper | Lower Limit
Debt Instrument [Line Items]
Commercial paper, maturity term		22 days	25 days
Commercial paper | Upper Limit
Debt Instrument [Line Items]
Commercial paper, maturity term		196 days	264 days