Revenue Recognition - Reconciliation of Contract Balances (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Dec. 31, 2020
Reconciliation of Contract Balances
Notes and accounts receivable-trade (net of allowances of $345 in 2021 and $351 in 2020)	$ 6,458	$ 7,132
Notes and accounts receivable - trade, allowances	345	351
Contract assets	522	497
Deferred income (current)	14,197	12,833
Deferred income (noncurrent)	4,153	$ 4,301
Revenue recognized that was included in deferred income at the beginning of the period	$ 4,200

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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