Commitments and Contingencies (Details)	6 Months Ended
	Jun. 30, 2020 USD ($) location	Dec. 31, 2019 USD ($) location
Commitments and Contingencies Disclosure [Abstract]
Environmental liability	$ 54,000,000	$ 56,000,000
Current environmental liability	$ 15,000,000	$ 15,000,000
Known cleanup and remediation locations and projects | location	109	110
Number of sites - representative sample | location	15
Liability associated with those sites	$ 38,000,000
Environmental locations representative sample liability payout period, in years	5 years
Responsible locations with another party | location	11
Self-insured injury/damage to third parties - and above, per occurrence	$ 75,000,000
Self-insured injury/damage to third party - up to	1,100,000,000
Self-insured injury/damage to third parties - and above, per occurrence for specific perils	1,500,000,000
Self-insured NS owned property - and above, per occurrence	75,000,000
Self-insured NS owned property - up to	$ 275,000,000
Portion Of Potential Losses Within A Specified Range Covered By Third Party Insurer, As A Percentage	85.00%