Revenue Recognition - Reconciliation of Contract Balances (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Reconciliation of Contract Balances
Notes and accounts receivable - trade (net of allowances of $369 in 2020 and $299 in 2019)	$ 6,543	$ 7,870
Notes and accounts receivable - trade, allowances	369	299
Contract assets	505	492
Deferred income (current)	12,469	12,026
Deferred income (noncurrent)	3,787	3,851
Revenue recognized that was included in deferred income at the beginning of the period	$ 4,500	$ 6,500