Components of Deferred Tax Assets / (Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Components of Deferred Tax Assets and Liabilities [Abstract]
Deferred Tax Liabilities, Property and Equipment	$ (14,313)	$ (13,860)
Deferred Tax Liabilities, Operating Lease Right-Of-Use-Assets	(492)
Deferred Tax Liabilities, Other	(524)	(346)
Total Deferred Tax Liabilities	15,329	14,206
Deferred Tax Assets, Operating Lease Liabilities	475
Deferred Tax Assets, Compensation and Benefits	158	165
Deferred Tax Assets, Casualty and environmental	114	122
Deferred Tax Assets, Other	229	124
Total Deferred Tax Assets	976	411
Net Deferred Tax Liability	$ 14,353	$ 13,795