Revenue Recognition - Reconciliation of Contract Balances (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Reconciliation of Contract Balances
Notes and accounts receivable - trade (net of allowances)	$ 7,414		$ 7,414		$ 7,432
Notes and accounts receivable - trade, allowances	281		281		309
Contract assets	594		594		470
Deferred income (current)	11,261		11,261		11,165
Deferred income (noncurrent)	3,474		3,474		$ 3,445
Revenue recognized that was included in deferred income at the beginning of the period	$ 3,800	$ 4,000	$ 5,700	$ 6,000