Commitments And Contingencies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Liability Activity [Abstract]
Commitments and contingencies, current portion, ending balance at December 31	$ 249	$ 207
Environmental [Abstract]
Beginning balance at January 1	171	170	172
Accruals	56	58	48
Payments	(45)	(57)	(50)
Ending balance at December 31	182	171	170
Current portion, ending balance at December 31	60	53	50
Sites identified which we are or may be liable for remediation costs	270unp_SitesIdentified
Sites subject of actions taken by the U.S. government	29
Sites on the Superfund National Priorities List	16
Personal Injury [Member]
Liability Activity [Abstract]
Commitments and contingencies, beginning balance	294	334	368
Accruals/(credits)	96	87	121
Changes in estimates for prior years	9	(38)	(58)
Payments	(64)	(89)	(97)
Commitments and contingencies, ending balance at December 31	335	294	334
Commitments and contingencies, current portion, ending balance at December 31	111	82	95
Reasonably possible outcome of related claims, range minimum	335
Reasonably possible outcome of related claims, range maximum	368
Asserted And Unasserted Claims [Abstract]
Percent of liability recorded related to asserted claims	93.00%
Percent of liability recorded related to unasserted claims	7.00%
Asbestos Issue [Member]
Liability Activity [Abstract]
Commitments and contingencies, beginning balance	131	139	147
Accruals/(credits)	1	2	(2)
Payments	(6)	(10)	(6)
Commitments and contingencies, ending balance at December 31	126	131	139
Commitments and contingencies, current portion, ending balance at December 31	8	9	8
Reasonably possible outcome of related claims, range minimum	126
Reasonably possible outcome of related claims, range maximum	135
Asserted And Unasserted Claims [Abstract]
Percent of liability recorded related to asserted claims	21.00%
Percent of liability recorded related to unasserted claims	79.00%
Guarantees [Member]
Guarantees [Abstract]
Maximum potential amount of guarantee payments	82	299
Recorded liability for fair value of guarantees	$ 0.3	$ 1.0
Expiration year of final guarantee	The final guarantee expires in 2022.

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Sites identified at which Railroad is or may be liable for remediation costs associated with alleged contamination or for violations of environmental requirements.

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Total costs accrued as of the balance sheet date for environmental loss contingencies.

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The aggregate amount disbursed during the reporting period to settle environmental loss contingencies.

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The amount added to the accrual for newly incurred environmental loss contingencies. These additions include remediation expense and interest accretion. These additions do not relate to changes in the environmental accrual related to a business acquisition or divestiture, to currency movements, or revisions in previously existing estimates.

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Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable in twelve months or in the next operating cycle if longer.

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The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

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