CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Operating Activities:
Net income	$ 214.0	$ 156.4
Adjustments to reconcile net income to cash provided by operations:
Depreciation and amortization	238.7	242.4
Amortization of deferred costs	4.3	6.3
Asset impairment	0.0	0.1
Net gain on sale of operating assets	(0.1)	(0.2)
Changes in operating assets and liabilities:
Trade and other receivables	10.0	7.2
Gas receivables and storage assets	0.0	(14.6)
Costs recoverable from customers	0.0	0.2
Other assets	(7.1)	(1.7)
Trade and other payables	(27.0)	8.1
Other payables, affiliates	(0.1)	(0.7)
Gas payables	2.9	(0.7)
Accrued liabilities	28.7	5.8
Other liabilities	(10.1)	21.6
Net cash provided by operating activities	454.2	430.2
Investing Activities:
Capital expenditures	(432.4)	(241.1)
Proceeds from sale of operating assets	0.2	0.3
Proceeds from other recoveries	0.0	6.2
Net cash used in investing activities	(432.2)	(234.6)
Financing Activities:
Proceeds from long-term debt, net of issuance cost	539.1	247.1
Repayment of borrowings from long-term debt and term loan	0.0	(725.0)
Proceeds from borrowings on revolving credit agreement	255.0	980.0
Repayment of borrowings on revolving credit agreement, including financing fees	(630.8)	(738.6)
Principal payment of capital lease obligation	(0.3)	(0.3)
Advances from affiliates	0.0	0.6
Distributions paid	(76.7)	(76.0)
Proceeds from sale of common units	0.0	113.1
Capital contributions from general partner	0.0	2.3
Net cash provided by (used in) financing activities	86.3	(196.8)
Increase (decrease) in cash and cash equivalents	108.3	(1.2)
Cash and cash equivalents at beginning of period	3.1	6.6
Cash and cash equivalents at end of period	$ 111.4	$ 5.4