Investments (Unaudited) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Available-for-sale securities	$ 68		$ 68		$ 175
Held-to-maturity securities	84		84		108
Total short-term investments	152		152		283
Investment in Conrail	980		980		959
Expenses for the use of the Shared Assets Area	32	30	97	88
Equity in the earnings of Conrail	8	3	21	16
Due to affiliate, current	166		166		128
Due to affiliate, noncurrent	133		133		133
Due to affiliate, noncurrent, maturity date	2035		2035		2035
Due to affiliate average interest rate	4.40%		4.40%		4.40%
Certificates of Deposit [Member]
Available-for-sale securities	10		10		76
Corporate Bonds [Member]
Available-for-sale securities	43		43		64
Held-to-maturity securities	41		41		59
Commercial Paper [Member]
Available-for-sale securities	0		0		35
Federal Government Bonds [Member]
Available-for-sale securities	15		15		0
Held-to-maturity securities	$ 43		$ 43		$ 49
Conrail Equity [Member]
Equity method investment, ownership percentage	58.00%		58.00%		58.00%
Conrail Voting [Member]
Equity method investment, ownership percentage	50.00%		50.00%		50.00%

This element is used to disclose the average interest rate associated with long-term advances from an affiliate.

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Total of debt securities categorized neither as held-to-maturity nor trading which are intended be sold or mature within one year from the balance sheet date or the normal operating cycle, whichever is longer.

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