Components of Deferred Tax Assets / (Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Components of Deferred Tax Assets and Liabilities [Abstract]
Deferred Tax Liabilities, Property and Equipment	$ (14,953)	$ (14,622)
Deferred Tax Liabilities, Operating Lease Right-Of-Use-Assets	(314)	(393)
Deferred Tax Liabilities, Other	(621)	(489)
Deferred Tax Liabilities, Gross	(15,888)	(15,504)
Deferred Tax Assets, Operating Lease Liabilities	315	386
Deferred Tax Assets, Compensation and Benefits	202	165
Deferred Tax Assets, Casualty and environmental	105	104
Deferred Tax Assets, Other	110	223
Total Deferred Tax Assets	732	878
Deferred Tax Liabilities, Net	$ (15,156)	$ (14,626)