Properties - Schedule of Net Properties (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 45,530	$ 45,100	[1]
Accumulated Depreciation	(13,086)	(12,932)	[1]
Properties - Net (Note 6)	32,444	32,168	[1]
Total Road
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	33,109	32,125
Accumulated Depreciation	(9,138)	(8,618)
Properties - Net (Note 6)	23,971	23,507
Rail and Other Track Material
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	8,449	8,194
Accumulated Depreciation	(1,739)	(1,719)
Properties - Net (Note 6)	$ 6,710	$ 6,475
Annual Depreciation Rate	2.50%	2.50%
Estimated useful life (Avg. Years)	41 years	40 years
Ties
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 6,284	$ 6,041
Accumulated Depreciation	(1,780)	(1,666)
Properties - Net (Note 6)	$ 4,504	$ 4,375
Annual Depreciation Rate	3.50%	3.70%
Estimated useful life (Avg. Years)	28 years	27 years
Grading
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 2,768	$ 2,763
Accumulated Depreciation	(614)	(595)
Properties - Net (Note 6)	$ 2,154	$ 2,168
Annual Depreciation Rate	1.30%	1.40%
Estimated useful life (Avg. Years)	75 years	72 years
Ballast
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 3,238	$ 3,156
Accumulated Depreciation	(1,051)	(1,013)
Properties - Net (Note 6)	$ 2,187	$ 2,143
Annual Depreciation Rate	2.60%	2.70%
Estimated useful life (Avg. Years)	38 years	37 years
Bridges, Trestles, and Culverts
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 2,688	$ 2,529
Accumulated Depreciation	(380)	(334)
Properties - Net (Note 6)	$ 2,308	$ 2,195
Annual Depreciation Rate	1.70%	1.60%
Estimated useful life (Avg. Years)	60 years	61 years
Signals and Interlockers
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 3,170	$ 3,077
Accumulated Depreciation	(944)	(819)
Properties - Net (Note 6)	$ 2,226	$ 2,258
Annual Depreciation Rate	4.10%	4.00%
Estimated useful life (Avg. Years)	24 years	25 years
Buildings
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 1,366	$ 1,335
Accumulated Depreciation	(529)	(492)
Properties - Net (Note 6)	$ 837	$ 843
Annual Depreciation Rate	2.50%	2.50%
Estimated useful life (Avg. Years)	40 years	40 years
Other
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 5,146	$ 5,030
Accumulated Depreciation	(2,101)	(1,980)
Properties - Net (Note 6)	$ 3,045	$ 3,050
Annual Depreciation Rate	4.10%	4.20%
Estimated useful life (Avg. Years)	25 years	24 years
Total Equipment
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 10,227	$ 10,708
Accumulated Depreciation	(3,948)	(4,314)
Properties - Net (Note 6)	6,279	6,394
Locomotive
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	5,085	5,320
Accumulated Depreciation	(1,849)	(2,020)
Properties - Net (Note 6)	$ 3,236	$ 3,300
Annual Depreciation Rate	3.60%	3.60%
Estimated useful life (Avg. Years)	27 years	27 years
Freight Cars
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 2,557	$ 2,964
Accumulated Depreciation	(540)	(880)
Properties - Net (Note 6)	$ 2,017	$ 2,084
Annual Depreciation Rate	2.90%	2.90%
Estimated useful life (Avg. Years)	35 years	35 years
Work Equipment and Other
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 2,585	$ 2,424
Accumulated Depreciation	(1,559)	(1,414)
Properties - Net (Note 6)	$ 1,026	$ 1,010
Annual Depreciation Rate	8.20%	8.20%
Estimated useful life (Avg. Years)	12 years	12 years
Land
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 1,823	$ 1,836
Properties - Net (Note 6)	1,823	1,836
Construction In Progress
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	371	431
Properties - Net (Note 6)	$ 371	$ 431

[1] Certain prior year data has been reclassified to conform to the current presentation.