Nature of Operations and Significant Accounting Policies (Details) carload in Thousands, $ in Millions	1 Months Ended	12 Months Ended
	Nov. 30, 2020 USD ($) mi	Dec. 31, 2020 USD ($) employee terminal line_of_business railroad carload port_terminal state mi	Dec. 31, 2019 USD ($)	[1]	Dec. 31, 2018 USD ($)	[1]
Revenue from External Customer [Line Items]
Number of rail route miles | mi		19,500
Rail network states number | state		23
Number of ocean, river and lake ports serviced (over) | port_terminal		70
Number of short-line and regional railroads served (more than) | railroad		230
Revenue | $		$ 10,583	$ 11,937		$ 12,250
Number of primary lines of business | line_of_business		3
Number of employees | employee		19,300
Number of union employees | employee		15,700
Cost method, maximum percentage		20.00%
Pan Am
Revenue from External Customer [Line Items]
Number of rail route miles | mi	1,200
Number of partial interests in rail route miles | mi	600
Pan Am
Revenue from External Customer [Line Items]
Deposit paid to acquire business classified as other investing activities | $	$ 30
Merchandise business
Revenue from External Customer [Line Items]
Number of carloads | carload		2,500
Percentage of total volume		43.00%
Percentage of total revenue		67.00%
Intermodal business
Revenue from External Customer [Line Items]
Number of carloads | carload		2,700
Percentage of total volume		46.00%
Percentage of total revenue		16.00%
Number of terminals | terminal		30
Coal business
Revenue from External Customer [Line Items]
Number of carloads | carload		637
Percentage of total volume		11.00%
Percentage of total revenue		13.00%
Other business
Revenue from External Customer [Line Items]
Percentage of total revenue		4.00%

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