Current Expected Credit Loss (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($)
Cumulative effect of accounting change	$ (94)
Notes and accounts receivable, net of allowances - Financial Instruments under Topic 326	16,450
Notes and accounts receivable, allowances - Financial Instruments under Topic 326	148
Loans and long-term receivables, net of allowances - Financial Instruments under Topic 326	9,668
Loans and long-term receivables, allowances - Financial Instruments under Topic 326	436
ExxonMobil Share Of Earnings Reinvested [Member]
Cumulative effect of accounting change	$ (93)