Income Taxes Components of Deferred Tax Assets / (Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Components of Deferred Tax Assets and Liabilities [Line Items]
Deferred Tax Liabilities, Property and Equipment	$ (20,634)	$ (19,660)
Deferred Tax Liabilities, Other	(340)	(341)
Deferred Tax Liabilities, Gross	(20,974)	(20,001)
Deferred Tax Assets, Compensation and Benefits	334	328
Deferred Tax Assets, Casualty and environmental	278	293
Deferred Tax Asset, Pension and Retiree Health and Welfare Benefits	89	126
Deferred Tax Assets, Long-term Debt Fair Value Adjustment Under Acquisition Method Accounting	76	96
Deferred Tax Asset, Intangible Assets and Liabilities	72	100
Deferred Tax Assets, Other	259	231
Deferred Tax Assets, Gross	1,108	1,174
Deferred Tax Liabilities, Net	(19,866)	(18,827)
Deferred Tax Liabilities, Net, Noncurrent	(19,866)	(19,072)
Current Portion of Deferred Income Taxes	$ 0	$ 245