Financial Instruments Long Term Debt (Details) - Exxon Mobil Corporation [Member] $ in Millions	Sep. 30, 2020 USD ($)
Debt Instrument [Line Items]
Long-term debt issued	$ 23,421
2.992% Notes Due 2025 (Issued March 2020) [Member] | Other U.S. Dollar Obligations [Member]
Debt Instrument [Line Items]
Long-term debt issued	$ 1,500
Interest rate	2.992%
3.294% Notes Due 2027 (Issued March 2020) [Member] | Other U.S. Dollar Obligations [Member]
Debt Instrument [Line Items]
Long-term debt issued	$ 1,000
Interest rate	3.294%
3.482% Notes Due 2030 (Issued March 2020) [Member] | Other U.S. Dollar Obligations [Member]
Debt Instrument [Line Items]
Long-term debt issued	$ 2,000
Interest rate	3.482%
4.227% Notes Due 2040 (Issued March 2020) [Member] | Other U.S. Dollar Obligations [Member]
Debt Instrument [Line Items]
Long-term debt issued	$ 1,250
Interest rate	4.227%
4.327% Notes Due 2050 (Issued March 2020) [Member] | Other U.S. Dollar Obligations [Member]
Debt Instrument [Line Items]
Long-term debt issued	$ 2,750
Interest rate	4.327%
1.571% Notes Due 2023 (Issued April 2020) [Member] | Other U.S. Dollar Obligations [Member]
Debt Instrument [Line Items]
Long-term debt issued	$ 2,750
Interest rate	1.571%
2.992% Notes Due 2025 (Issued April 2020) [Member] | Other U.S. Dollar Obligations [Member]
Debt Instrument [Line Items]
Long-term debt issued	$ 1,310
Interest rate	2.992%
2.610% Notes Due 2030 (Issued April 2020) [Member] | Other U.S. Dollar Obligations [Member]
Debt Instrument [Line Items]
Long-term debt issued	$ 2,000
Interest rate	2.61%
4.227% Notes Due 2040 (Issued April 2020) [Member] | Other U.S. Dollar Obligations [Member]
Debt Instrument [Line Items]
Long-term debt issued	$ 842
Interest rate	4.227%
3.452% Notes Due 2051 (Issued April 2020) [Member] | Other U.S. Dollar Obligations [Member]
Debt Instrument [Line Items]
Long-term debt issued	$ 2,750
Interest rate	3.452%
2.992% Notes Due 2025 and 4.227% Notes Due 2040 (Issued April 2020) [Member]
Debt Instrument [Line Items]
Debt Instrument, Unamortized Premium	$ 152
0.142% Notes Due 2024 (Issued June 2020) [Member] | Other Foreign Currency Obligations [Member]
Debt Instrument [Line Items]
Long-term debt issued	$ 1,756
Interest rate	0.142%
0.524% Notes Due 2028 (Issued June 2020) [Member] | Other Foreign Currency Obligations [Member]
Debt Instrument [Line Items]
Long-term debt issued	$ 1,171
Interest rate	0.524%
0.835% Notes Due 2032 (Issued June 2020) [Member] | Other Foreign Currency Obligations [Member]
Debt Instrument [Line Items]
Long-term debt issued	$ 1,171
Interest rate	0.835%
1.408% Notes Due 2039 (Issued June 2020) [Member] | Other Foreign Currency Obligations [Member]
Debt Instrument [Line Items]
Long-term debt issued	$ 1,171
Interest rate	1.408%