Properties - Schedule of Net Properties (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 45,100	$ 44,805
Accumulated Depreciation	(12,932)	(12,807)
Properties - Net (Note 6)	32,168	31,998
Total Road
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	32,125	31,411
Accumulated Depreciation	(8,618)	(8,323)
Properties - Net (Note 6)	23,507	23,088
Rail and Other Track Material
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	8,194	7,964
Accumulated Depreciation	(1,719)	(1,698)
Properties - Net (Note 6)	$ 6,475	$ 6,266
Annual Depreciation Rate	2.50%	2.50%
Estimated useful life (Avg. Years)	40 years	40 years
Ties
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 6,041	$ 5,860
Accumulated Depreciation	(1,666)	(1,557)
Properties - Net (Note 6)	$ 4,375	$ 4,303
Annual Depreciation Rate	3.70%	3.70%
Estimated useful life (Avg. Years)	27 years	27 years
Grading
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 2,763	$ 2,757
Accumulated Depreciation	(595)	(572)
Properties - Net (Note 6)	$ 2,168	$ 2,185
Annual Depreciation Rate	1.40%	1.40%
Estimated useful life (Avg. Years)	72 years	72 years
Ballast
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 3,156	$ 3,076
Accumulated Depreciation	(1,013)	(971)
Properties - Net (Note 6)	$ 2,143	$ 2,105
Annual Depreciation Rate	2.70%	2.70%
Estimated useful life (Avg. Years)	37 years	37 years
Bridges, Trestles, and Culverts
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 2,529	$ 2,506
Accumulated Depreciation	(334)	(382)
Properties - Net (Note 6)	$ 2,195	$ 2,124
Annual Depreciation Rate	1.60%	1.60%
Estimated useful life (Avg. Years)	61 years	61 years
Signals and Interlockers
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 3,077	$ 2,975
Accumulated Depreciation	(819)	(693)
Properties - Net (Note 6)	$ 2,258	$ 2,282
Annual Depreciation Rate	4.00%	4.00%
Estimated useful life (Avg. Years)	25 years	25 years
Buildings
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 1,335	$ 1,318
Accumulated Depreciation	(492)	(486)
Properties - Net (Note 6)	$ 843	$ 832
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	$ 5,030	$ 4,955
Accumulated Depreciation	(1,980)	(1,964)
Properties - Net (Note 6)	$ 3,050	$ 2,991
Annual Depreciation Rate	4.20%	4.20%
Estimated useful life (Avg. Years)	24 years	24 years
Total Equipment
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 10,708	$ 11,092
Accumulated Depreciation	(4,314)	(4,484)
Properties - Net (Note 6)	6,394	6,608
Locomotive
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	5,320	5,661
Accumulated Depreciation	(2,020)	(2,266)
Properties - Net (Note 6)	$ 3,300	$ 3,395
Annual Depreciation Rate	3.60%	3.50%
Estimated useful life (Avg. Years)	27 years	29 years
Freight Cars
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 2,964	$ 3,093
Accumulated Depreciation	(880)	(882)
Properties - Net (Note 6)	$ 2,084	$ 2,211
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	$ 2,424	$ 2,338
Accumulated Depreciation	(1,414)	(1,336)
Properties - Net (Note 6)	$ 1,010	$ 1,002
Annual Depreciation Rate	8.20%	7.40%
Estimated useful life (Avg. Years)	12 years	14 years
Land
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	$ 1,836	$ 1,845
Properties - Net (Note 6)	1,836	1,845
Construction In Progress
Property, Plant and Equipment, Net, by Type [Abstract]
Cost	431	457
Properties - Net (Note 6)	$ 431	$ 457