Debt (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Long-term debt
Debt Instrument, Face Amount	$ 13,971	$ 13,971
Finance Lease Obligations	720	777
Net unamortized premiums and discounts	204	220
Total debt	14,895	14,968
Short-term debt	(105)	(112)
Long-term debt	14,790	14,856
Variable rate debt bonds [Member]
Long-term debt
Debt Instrument, Face Amount	283	283
9.125% Debentures [Member] \| Due 2021 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	123	123
8.20% Debentures [Member] \| Due 2025 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	134	134
8.125% Notes [Member] \| Due 2030 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	390	390
7.9% Debentures [Member] \| Due 2047 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	60	60
7.8% Debentures [Member] \| Due 2027 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	203	203
7.65% Debentures [Member] \| Due 2023 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	78	78
7.40% Notes [Member] \| Due 2031 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	500	500
7.375% Debentures [Member] \| Due 2029 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	92	92
7.25% Notes [Member] \| Due 2031 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	500	500
7.20% Notes [Member] \| Due 2031 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	575	575
7% Debentures [Member] \| Due 2029 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	200	200
6.95% Notes [Member] \| Due 2029 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	1,549	1,549
6.875% Debentures [Member] \| Due 2026 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	67	67
6.50% Notes [Member] \| Due 2039 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	2,750	2,750
5.951% Notes [Member] \| Due 2037 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	645	645
5.95% Notes [Member] \| Due 2036 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	500	500
5.95% Notes [Member] \| Due 2046 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	500	500
5.90% Notes [Member] \| Due 2032 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	505	505
5.90% Notes [Member] \| Due 2038 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	600	600
4.95% Notes [Member] \| Due 2026 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	1,250	1,250
4.3% Notes [Member] \| Due 2044 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	750	750
4.15% Notes [Member] \| Due 2034 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	246	246
3.35% Notes [Member] \| Due 2024 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	426	426
3.35% Notes [Member] \| Due 2025 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	199	199
2.4% Notes [Member] \| Due 2022 [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	329	329
Floating rate note due 2018 [Member] \| Due 2018 [Member] \| Floating Rate Notes [Member]
Long-term debt
Debt Instrument, Face Amount	$ 500	$ 500
Floating Rate Notes Due 2022 [Member] \| Floating Rate Notes [Member] \| Minimum [Member]
Long-term debt
Debt Instrument, Interest Rate, Stated Percentage	2.81%	2.32%
Floating Rate Notes Due 2022 [Member] \| Floating Rate Notes [Member] \| Maximum [Member]
Long-term debt
Debt Instrument, Interest Rate, Stated Percentage	3.58%	3.52%
Industrial Development Bonds Due One [Member] \| Variable rate debt bonds [Member]
Long-term debt
Debt Instrument, Face Amount	$ 18	$ 18
Industrial Development Bonds Due One [Member] \| Variable rate debt bonds [Member] \| Minimum [Member]
Long-term debt
Debt Instrument, Interest Rate, Stated Percentage	1.08%	0.95%
Industrial Development Bonds Due One [Member] \| Variable rate debt bonds [Member] \| Maximum [Member]
Long-term debt
Debt Instrument, Interest Rate, Stated Percentage	2.45%	1.86%
Marine Terminal Revenue Refunding Bonds [Member] \| Variable rate debt bonds [Member] \| Minimum [Member]
Long-term debt
Debt Instrument, Interest Rate, Stated Percentage	1.08%	0.88%
Marine Terminal Revenue Refunding Bonds [Member] \| Variable rate debt bonds [Member] \| Maximum [Member]
Long-term debt
Debt Instrument, Interest Rate, Stated Percentage	2.45%	1.95%
Marine Terminal Revenue Refunding Bonds [Member] \| Due 2031 [Member] \| Variable rate debt bonds [Member]
Long-term debt
Debt Instrument, Face Amount	$ 265	$ 265
Other Debt [Member] \| Unsecured Debt (Debentures) [Member]
Long-term debt
Debt Instrument, Face Amount	$ 17	$ 17

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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