Income Taxes Components of Deferred Tax Assets / (Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Components of Deferred Tax Assets and Liabilities [Line Items]
Deferred Tax Liabilities, Property and Equipment	$ (17,727)	$ (17,330)
Deferred Tax Liabilities, Hedging	(11)	(10)
Deferred Tax Liability, Pension and Retiree Health and Welfare	(13)	0
Deferred Tax Liabilities, Other	(347)	(336)
Deferred Tax Liabilities, Gross	(18,098)	(17,676)
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits	371	358
Deferred Tax Assets, Tax Deferred Expense, Casualty and environmental	273	303
Deferred Tax Asset, Tax Deferred Expense, Intangible Assets and Liabilities	190	275
Deferred Tax Assets, Tax Deferred Expense, Long-term Debt Fair Value Adjustment	141	173
Deferred Tax Asset, Deferred Tax Expense, Pension and Retiree Health and Welfare Benefits	0	332
Deferred Tax Assets, Other	257	257
Deferred Tax Assets, Gross	1,232	1,698
Deferred Tax Liabilities, Net	(16,866)	(15,978)
Deferred Tax Liabilities, Net, Noncurrent	(17,224)	(16,319)
Deferred Tax Assets, Net, Current	$ 358	$ 341