Debt (Details 3) (USD $) In Millions, unless otherwise specified	0 Months Ended	3 Months Ended
Jun. 23, 2011	Jun. 30, 2011
Debt Exchange [Line Items]
Original debt	$ 857
New debt	750
New rate	4.163%
New due date	Jul. 15, 2022
Debt exchange fees		6
Cash consideration	267
Accrued and unpaid interest	17
7.875% Notes Due 2019 [Member]
Debt Exchange [Line Items]
Original debt	196
Original rate	7.875%
Original due date, year	2019
5.450% Notes Due 2013 [Member]
Debt Exchange [Line Items]
Original debt	50
Original rate	5.45%
Original due date, year	2013
5.125% Notes Due 2014 [Member]
Debt Exchange [Line Items]
Original debt	45
Original rate	5.125%
Original due date, year	2014
5.375% Notes Due 2014 [Member]
Debt Exchange [Line Items]
Original debt	55
Original rate	5.375%
Original due date, year	2014
5.700% Notes Due 2018 [Member]
Debt Exchange [Line Items]
Original debt	277
Original rate	5.70%
Original due date, year	2018
5.750% Notes Due 2017 [Member]
Debt Exchange [Line Items]
Original debt	178
Original rate	5.75%
Original due date, year	2017
7.000% Debentures Due 2016 [Member]
Debt Exchange [Line Items]
Original debt	38
Original rate	7.00%
Original due date, year	2016
5.560% Notes Due 2017 [Member]
Debt Exchange [Line Items]
Original debt	$ 18
Original rate	5.65%
Original due date, year	2017

Accrued interest paid to debtholder on the existing debt at date of exchange.

Name:	unp_AccruedInterestDebtExchangeExistingNotes
Namespace Prefix:	unp
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Cash paid to the debtholder as consideration for the exchange of the existing debt to new debt.

+ Details

Name:	unp_CashConsiderationDebtExchange
Namespace Prefix:	unp
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The value of the financial instrument(s) that the original debt is being converted into in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 95
-Paragraph 32
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586

+ Details

Name:	us-gaap_DebtConversionConvertedInstrumentAmount1
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The expiration, mandatory redemption, or due date, day, month and year (YYYY-MM-DD), of the financial instrument issued in exchange for the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

+ References

+ Details

Name:	us-gaap_DebtConversionConvertedInstrumentExpirationOrDueDateDayMonthAndYear
Namespace Prefix:	us-gaap
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

The dividend or interest rate, if any, associated with the financial instrument issued in exchange for the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

+ References

+ Details

Name:	us-gaap_DebtConversionConvertedInstrumentRate
Namespace Prefix:	us-gaap
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ Details

Name:	us-gaap_DebtConversionLineItems
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of the original debt being converted in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

+ References

+ Details

Name:	us-gaap_DebtConversionOriginalDebtAmount1
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The rate of interest that was being paid on the original debt issue that is being converted in the noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

+ References

+ Details

Name:	us-gaap_DebtConversionOriginalDebtInterestRateOfDebt
Namespace Prefix:	us-gaap
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The year (YYYY) in which the original debt was issued.

+ References

+ Details

Name:	us-gaap_DebtConversionOriginalDebtIssuanceDateOfDebtYear
Namespace Prefix:	us-gaap
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of debt issuance costs that were incurred during a noncash or partial noncash transaction.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 95
-Paragraph 32
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4313-108586

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

+ Details

Name:	us-gaap_DebtIssuanceCostsIncurredDuringNoncashOrPartialNoncashTransaction
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration