Properties (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Cost	$ 64,146		$ 63,214
Accumulated depreciation	17,218		16,942
Net book value	46,928		46,272
Land [Member]
Property, Plant and Equipment [Line Items]
Cost	5,215		5,194
Net book value	5,215		5,194
Road: Rail and Other Track Material [Member]
Property, Plant and Equipment [Line Items]
Cost	14,745		14,588
Accumulated depreciation	5,307		5,241
Net book value	9,438		9,347
Estimated useful life	37 years		33 years
Road: Ties [Member]
Property, Plant and Equipment [Line Items]
Cost	9,194		9,102
Accumulated depreciation	2,495		2,450
Net book value	6,699		6,652
Estimated useful life	33 years		33 years
Road: Ballast [Member]
Property, Plant and Equipment [Line Items]
Cost	4,869		4,826
Accumulated depreciation	1,288		1,264
Net book value	3,581		3,562
Estimated useful life	34 years		34 years
Road: Other Roadway [Member]
Property, Plant and Equipment [Line Items]
Cost	16,615	[1]	16,476	[1]
Accumulated depreciation	2,898	[1]	2,852	[1]
Net book value	13,717	[1]	13,624	[1]
Estimated useful life	47 years	[1]	47 years	[1]
Road [Member]
Property, Plant and Equipment [Line Items]
Cost	45,423		44,992
Accumulated depreciation	11,988		11,807
Net book value	33,435		33,185
Equipment: Locomotives [Member]
Property, Plant and Equipment [Line Items]
Cost	8,587		8,276
Accumulated depreciation	3,775		3,694
Net book value	4,812		4,582
Estimated useful life	20 years		20 years
Equipment: Freight Cars [Member]
Property, Plant and Equipment [Line Items]
Cost	2,106		2,116
Accumulated depreciation	968		968
Net book value	1,138		1,148
Estimated useful life	25 years		25 years
Equipment: Work Equipment and Other [Member]
Property, Plant and Equipment [Line Items]
Cost	742		684
Accumulated depreciation	161		153
Net book value	581		531
Estimated useful life	18 years		18 years
Equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	11,435		11,076
Accumulated depreciation	4,904		4,815
Net book value	6,531		6,261
Technology and Other [Member]
Property, Plant and Equipment [Line Items]
Cost	899		872
Accumulated depreciation	326		320
Net book value	573		552
Estimated useful life	11 years		10 years
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Cost	1,174		1,080
Net book value	$ 1,174		$ 1,080

[1] Other roadway includes grading, bridges and tunnels, signals, buildings, and other road assets.