Receivables - Additional Information (Details) $ in Millions		12 Months Ended
	Mar. 30, 2012 USD ($)	Dec. 31, 2018 USD ($) financial_institution	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Schedule Of Financial Receivables [Line Items]
Number of arrangement with different financial institution to sell customer receivables | financial_institution		3
Funding of customer receivables sold		$ 0	$ 0
Sale of customer receivables	$ 304
Cash received for receivables	50	1,016	792	$ 778
Deferred purchase price receivable	$ 254	234	187
Net cash funding received during the period		300
Amount of cash draws under arrangement during the period		2,958
Amount of cash repayments under arrangement during the period		(2,658)
Amount of cash draws under arrangement since inception		600	600
Amount of cash repayments under arrangement since inception		(600)	(600)
Gross amount of receivables sold under the deferred purchase program		41,784
Cash collections of other receivables		41,200
Gross cash outflows from deferred purchased receivables		6,375	5,471
Gross cash inflow from deferred purchase receivable		(6,328)	$ (5,367)
Maximum
Schedule Of Financial Receivables [Line Items]
Funding of customer receivables sold		$ 400