v3.19.3.a.u2
Long-Term Debt (Summarized Long-Term Debt) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Long-term Debt [Line Items]    
Debt issuance costs $ (60) $ (42)
Long-term debt 26,342 20,538
XTO Energy Inc. [Member]    
Long-term Debt [Line Items]    
Debt instrument, unamortized premium 92 97
Combined Exxon Mobil And Affiliates [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Other long-term debt 89 102
Combined Exxon Mobil And Affiliates [Member] | Other Foreign Currency Obligations [Member]    
Long-term Debt [Line Items]    
Other long-term debt 64 38
1.912% Notes Due 2020 [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent   $ 1,500
Interest rate   1.912%
Debt maturity   Mar. 06, 2020
2.222% Notes Due 2021 [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 2,500 $ 2,500
Interest rate 2.222%  
Debt maturity Mar. 01, 2021 Mar. 01, 2021
2.397% Notes Due 2022 (Issued 2015) [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 1,150 $ 1,150
Interest rate 2.397%  
Debt maturity Mar. 06, 2022 Mar. 06, 2022
1.902% Notes Due 2022 (Issued 2019) [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 750  
Interest rate 1.902%  
Debt maturity Aug. 16, 2022  
Floating-Rate Notes Due 2022 (Issued 2015) [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 500 $ 500
Debt maturity Mar. 06, 2022 Mar. 06, 2022
Average effective interest rate [1] 2.792%  
Floating-Rate Notes Due 2022 (Issued 2019) [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 750  
Debt maturity Aug. 16, 2022  
Average effective interest rate [1] 2.414%  
2.726% Notes Due 2023 [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 1,250 $ 1,250
Interest rate 2.726%  
Debt maturity Mar. 01, 2023 Mar. 01, 2023
3.176% Notes Due 2024 (Issued 2014) [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 1,000 $ 1,000
Interest rate 3.176%  
Debt maturity Mar. 15, 2024 Mar. 15, 2024
2.019% Notes Due 2024 (Issued 2019) [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 1,000  
Interest rate 2.019%  
Debt maturity Aug. 16, 2024  
2.709% Notes Due 2025 [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 1,750 $ 1,750
Interest rate 2.709%  
Debt maturity Mar. 06, 2025 Mar. 06, 2025
3.043% Notes Due 2026 (Issued 2016) [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 2,500 $ 2,500
Interest rate 3.043%  
Debt maturity Mar. 01, 2026 Mar. 01, 2026
2.275% Notes Due 2026 (Issued 2019) [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 1,000  
Interest rate 2.275%  
Debt maturity Aug. 16, 2026  
2.440% Notes Due 2029 [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 1,250  
Interest rate 2.44%  
Debt maturity Aug. 16, 2029  
2.995% Notes Due 2039 [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 750  
Interest rate 2.995%  
Debt maturity Aug. 16, 2039  
3.567% Notes Due 2045 [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 1,000 $ 1,000
Interest rate 3.567%  
Debt maturity Mar. 06, 2045 Mar. 06, 2045
4.114% Notes Due 2046 [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 2,500 $ 2,500
Interest rate 4.114%  
Debt maturity Mar. 01, 2046 Mar. 01, 2046
3.095% Notes Due 2049 [Member] | Exxon Mobil Corporation [Member] | Other U.S. Dollar Obligations [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 1,500  
Interest rate 3.095%  
Debt maturity Aug. 16, 2049  
6.100% Senior Notes Due 2036 [Member] | XTO Energy Inc. [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 193 $ 195
Interest rate 6.10%  
Debt maturity Apr. 01, 2036 Apr. 01, 2036
6.750% Senior Notes Due 2037 [Member] | XTO Energy Inc. [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 296 $ 299
Interest rate 6.75%  
Debt maturity Aug. 01, 2037 Aug. 01, 2037
6.375% Senior Notes Due 2038 [Member] | XTO Energy Inc. [Member]    
Long-term Debt [Line Items]    
Senior notes, noncurrent $ 229 $ 230
Interest rate 6.375%  
Debt maturity Jun. 15, 2038 Jun. 15, 2038
8.625% Debentures Due 2021 [Member] | Mobil Corporation [Member]    
Long-term Debt [Line Items]    
Other long-term debt $ 250 $ 250
Interest rate 8.625%  
Debt maturity Aug. 15, 2021 Aug. 15, 2021
Industrial Revenue Bonds Due 2020-2051 [Member] | Combined Exxon Mobil And Affiliates [Member]    
Long-term Debt [Line Items]    
Other long-term debt $ 2,461 $ 2,513
Debt instrument, maturity date range, start Jun. 01, 2020 Jun. 01, 2020
Debt instrument, maturity date range, end Dec. 01, 2051 Dec. 01, 2051
Average effective interest rate [1] 1.388%  
Finance Lease Obligations [Member] | Combined Exxon Mobil And Affiliates [Member]    
Long-term Debt [Line Items]    
Average effective interest rate [1] 9.518%  
Finance lease obligations $ 1,670 $ 1,303
[1] Average effective interest rate for debt and average imputed interest rate for finance leases at December 31, 2019.