Equity Method Investments - Narrative (Details)	1 Months Ended		12 Months Ended
	Feb. 28, 2014 mi	Apr. 30, 2012 USD ($) mi	Dec. 31, 2015 USD ($) investment
Schedule of Equity Method Investments [Line Items]
Equity Method Investments, Number of Investments | investment			2
Transcontinental Gas Pipe Line Company LLC
Schedule of Equity Method Investments [Line Items]
Entity's equity interest in construction agreement (as a percent)	61.00%
Constitution Pipeline Company, LLC
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)		25.00%
Length of pipeline to be constructed (in miles) | mi		124
Contribution cap		$ 250,000,000
Expected contribution in future years			$ 139,000,000
Number of year's investment expected for contribution			2 years
Meade Pipeline Co LLC
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	20.00%
Length of pipeline to be constructed (in miles) | mi	177
Expected contribution in future years			$ 130,200,000
Number of year's investment expected for contribution			2 years
Entity's equity interest in construction agreement (as a percent)	39.00%