CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
OPERATING ACTIVITIES:
Net income	$ 295.7	$ 240.3	$ 297.0
Adjustments to reconcile net income to cash provided by operations:
Depreciation and amortization	346.1	344.7	322.8
Amortization of deferred costs and other	13.1	8.9	8.1
(Gain) loss on sale of assets and impairments	(3.2)	(0.2)	49.0
Changes in operating assets and liabilities:
Trade and other receivables	21.2	(20.4)	6.1
Gas receivables and storage assets	(27.6)	12.6	5.6
Costs recoverable from customers	19.2	(23.6)	3.8
Other assets	0.4	(1.1)	(3.8)
Trade and other payables	2.9	(0.2)	(14.0)
Gas payables	(0.1)	1.2	(5.8)
Accrued liabilities	1.7	6.0	(4.1)
Other liabilities	(7.4)	(2.6)	(27.7)
Net cash provided by operating activities	662.0	565.6	637.0
INVESTING ACTIVITIES:
Capital expenditures	(429.0)	(486.7)	(708.4)
Proceeds from sale of operating assets	5.7	1.0	63.8
Advances to affiliates	0.0	(0.1)	0.0
Net cash used in investing activities	(423.3)	(485.8)	(644.6)
FINANCING ACTIVITIES:
Proceeds from long-term debt, net of issuance cost	495.2	0.0	494.0
Repayment of borrowings from long-term debt	(350.0)	(185.0)	(575.0)
Proceeds from borrowings on revolving credit agreement	660.0	640.0	765.0
Repayment of borrowings on revolving credit agreement, including financing fees	(945.0)	(445.0)	(560.8)
Principal payment of finance lease obligation	(0.7)	(0.6)	(0.5)
Advances from affiliates	4.1	(1.0)	0.1
Distributions paid	(102.2)	(102.2)	(102.2)
Net cash (used in) provided by financing activities	(238.6)	(93.8)	20.6
Increase (decrease) in cash and cash equivalents	0.1	(14.0)	13.0
Cash and cash equivalents at beginning of period	3.6	17.6	4.6
Cash and cash equivalents at end of period	$ 3.7	$ 3.6	$ 17.6