Revenues - Revenues Disaggregated by Lines of Business (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 2,990	$ 2,255	$ 5,803	$ 5,110
Total Merchandise
Disaggregation of Revenue [Line Items]
Revenue	1,903	1,508	3,721	3,435
Chemicals
Disaggregation of Revenue [Line Items]
Revenue	606	531	1,186	1,157
Agricultural and Food Products
Disaggregation of Revenue [Line Items]
Revenue	370	311	719	676
Forest Products
Disaggregation of Revenue [Line Items]
Revenue	233	197	453	416
Automotive
Disaggregation of Revenue [Line Items]
Revenue	216	93	452	374
Metals and Equipment
Disaggregation of Revenue [Line Items]
Revenue	204	142	390	341
Minerals
Disaggregation of Revenue [Line Items]
Revenue	152	134	277	261
Fertilizers
Disaggregation of Revenue [Line Items]
Revenue	122	100	244	210
Intermodal
Disaggregation of Revenue [Line Items]
Revenue	511	359	979	781
Coal
Disaggregation of Revenue [Line Items]
Revenue	423	287	807	692
Other
Disaggregation of Revenue [Line Items]
Revenue	$ 153	$ 101	$ 296	$ 202