Revenue Recognition - Reconciliation of Contract Balances (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
Reconciliation of Contract Balances
Notes and accounts receivable - trade (net of allowances of $277 in 2021 and $351 in 2020)	$ 6,609	$ 6,609	$ 7,132
Notes and accounts receivable - trade, allowances	277	277	351
Contract assets	566	566	497
Deferred income (current)	12,264	12,264	12,833
Deferred income (noncurrent)	3,965	3,965	$ 4,301
Revenue recognized that was included in deferred income at the beginning of the period	$ 5,100	$ 9,500

Amount, after allowance for credit loss, of right to consideration from customer for product sold and service rendered in normal course of business, classified as current.

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Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time, classified as current.

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