Partners' Capital and Distributions (Details 5) (USD $) In Millions, except Per Share data, unless otherwise specified	1 Months Ended	9 Months Ended
	Feb. 29, 2012	Sep. 30, 2012 Bcf
PNG
Performance Thresholds
General partner ownership interest (as a percent)		2.00%
Series B Subordinated Units
Performance Thresholds
Number of distinct tranches		5
Series B Subordinated Units | Tranche 1 | PNG
Performance Thresholds
Previous annualized distribution benchmark (in dollars per unit)	$ 1.44
Series B subordinated units that will convert into Series A subordinated units		2.6
Working gas storage capacity (in Bcf)		29.6
Annualized distribution level (in dollars per unit)		$ 1.71
Series B Subordinated Units | Tranche 2 | PNG
Performance Thresholds
Previous annualized distribution benchmark (in dollars per unit)	$ 1.53
Series B subordinated units that will convert into Series A subordinated units		2.8
Working gas storage capacity (in Bcf)		35.6
Annualized distribution level (in dollars per unit)		$ 1.71
Series B Subordinated Units | Tranche 3 | PNG
Performance Thresholds
Previous annualized distribution benchmark (in dollars per unit)	$ 1.63
Series B subordinated units that will convert into Series A subordinated units		2.1
Working gas storage capacity (in Bcf)		41.6
Annualized distribution level (in dollars per unit)		$ 1.71
Series B Subordinated Units | Tranche 4 | PNG
Performance Thresholds
Series B subordinated units that will convert into Series A subordinated units		3.0
Working gas storage capacity (in Bcf)		48.0
Annualized distribution level (in dollars per unit)		$ 1.71
Series B Subordinated Units | Tranche 5 | PNG
Performance Thresholds
Series B subordinated units that will convert into Series A subordinated units		3.0
Working gas storage capacity (in Bcf)		48.0
Annualized distribution level (in dollars per unit)		$ 1.80