Related Party Transactions - Schedule of Other Contribution from Parent (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Contribution of JV Partner payment	$ 0.0	$ 4.5
Reimbursement of project	1.6	0.0
Total contributions	3.0	12.9
Cash contribution received from Parent	2.8	11.1
Contribution receivable from Parent	0.2	1.8	$ 0.0
SPLC
Related Party Transaction [Line Items]
Reimbursement of project	0.0	1.8
Mars
Related Party Transaction [Line Items]
Mars cavern integrity project indemnification	0.0	2.9
Zydeco
Related Party Transaction [Line Items]
Reimbursement of Zydeco directional drill	1.4	2.3
Reimbursement for Zydeco FERC rate case	$ 0.0	$ 1.4