UNIT-BASED COMPENSATION Narrative 2 (Details) (The 2006 LTIP [Member], USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Unit options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
NSH unit options, description	On November 16, 2007, we granted 324,100 NSH unit options at $31.55, which was our only grant of options under the 2006 LTIP.
NSH unit options, terms	These options expire seven years from the grant date and vest in annual one-third increments beginning on November 16, 2010.
NSH unit options, units exercised	11,667	0	11,667
The total intrinsic value of unit options exercised during the period	$ 0.1		$ 0.1
Balance of NSH unit options outstanding	300,766	312,433
Restricted units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value of restricted units	$ 28.77	30.53	$ 36.54
Total fair value of NSH restricted units that vested during the period	$ 1.0	0.7	$ 0.8