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Investments (Details) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
Investments (Details) $ in Millions	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) railroad	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Schedule of Investments [Line Items]
Number of North American railroads \| railroad			8
Equity Method Investee
Schedule of Investments [Line Items]
Equity method investment, ownership percentage	58.00%		58.00%
Conrail Voting
Schedule of Investments [Line Items]
Equity method investment, ownership percentage	50.00%		50.00%
Conrail Inc
Schedule of Investments [Line Items]
Equity method investments	$ 1,500		$ 1,500		$ 1,400
Expenses from transactions with related party	37	$ 30	71	$ 65
Equity in the earnings of investee	14	13	28	22
Due to affiliate, noncurrent	$ 534		$ 534		$ 534
Due to affiliate, average interest rate			1.31%		1.31%
TTX Company
Schedule of Investments [Line Items]
Equity method investment, ownership percentage	19.65%		19.65%
Expenses from transactions with related party	$ 61	58	$ 124	118
Equity in the earnings of investee	$ 14	$ 10	$ 31	$ 14