Revenue Recognition - Reconciliation of Contract Balances (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021	Dec. 31, 2020
Reconciliation of Contract Balances
Notes and accounts receivable - trade (net of allowances of $300 in 2021 and $351 in 2020)	$ 6,827	$ 6,827	$ 7,132
Notes and accounts receivable - trade, allowances	300	300	351
Contract assets	547	547	497
Deferred income (current)	13,272	13,272	12,833
Deferred income (noncurrent)	4,113	4,113	$ 4,301
Revenue recognized that was included in deferred income at the beginning of the period	$ 4,900	$ 7,200