Commitments and Contingencies - Schedule of Number of Locomotives and Payments under Long-term Maintenance Program (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) locomotive	Dec. 31, 2019 USD ($) locomotive	Dec. 31, 2018 USD ($) locomotive
Commitments and Contingencies Disclosure [Abstract]
Amounts Paid | $	$ 158	$ 139	$ 170
Number of Locomotives | locomotive	1,874	1,897	1,910