Commitments and Contingencies (Unaudited) (Details) (USD $)	3 Months Ended
	Sep. 30, 2011	Mar. 31, 2011	Mar. 31, 2010	Dec. 31, 2010
Commitments and Contingencies [Abstract]
Arbitration claim settlement			$ 100,000,000
Contested portion of arbitration		43,000,000
Arbitration decision expense		43,000,000
Other arbitration expense		15,000,000
Environmental liability	32,000,000			33,000,000
Current environmental liability	12,000,000			12,000,000
Known cleanup and remediation locations and projects	154
Number of sites	7
Liability associated with those sites	11,000,000
Environmental locations representative sample liability payout period, in years	5
Responsible locations with another party	31
Self-insured injury/damage to third party - up to	50,000,000
Self-insured injury/damage to third parties - and above, per occurrence	1,000,000,000
Self-insured NS owned property - up to	25,000,000
Self-insured NS owned property - and above, per occurrence	175,000,000
Purchase commitments, long-term service contracts	$ 813,000,000