CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
OPERATING ACTIVITIES:
Net income	$ 315.0	$ 290.5	$ 295.7
Adjustments to reconcile net income to cash provided by operations:
Depreciation and amortization	366.3	358.8	346.1
Amortization of deferred costs and other	9.0	12.4	13.1
(Gain) loss on sale of assets and impairments	(0.1)	0.9	(3.2)
Changes in operating assets and liabilities:
Trade and other receivables	(19.1)	(6.1)	21.2
Gas transportation receivables and storage assets	(32.8)	(9.0)	(27.6)
Other assets	(2.7)	(4.5)	0.4
Trade and other payables	1.1	(10.6)	2.9
Gas transportation payables	9.3	1.4	(0.1)
Accrued liabilities	(1.3)	4.7	1.7
Regulatory assets and liabilities	(4.1)	4.8	20.7
Other liabilities	(11.3)	(2.1)	(8.9)
Net cash provided by operating activities	629.3	641.2	662.0
INVESTING ACTIVITIES:
Capital expenditures	(349.2)	(438.2)	(429.0)
Proceeds from sale of operating assets	1.7	3.8	5.7
Net cash used in investing activities	(347.5)	(434.4)	(423.3)
FINANCING ACTIVITIES:
Proceeds from long-term debt, net of issuance cost	0.0	495.0	495.2
Repayment of borrowings from long-term debt	0.0	(440.0)	(350.0)
Proceeds from borrowings on revolving credit facility	150.0	687.9	660.0
Repayment of borrowings on revolving credit facility, including financing fees	(284.4)	(852.9)	(945.0)
Principal payment of finance lease obligation	(0.8)	(0.7)	(0.7)
Advances from affiliates	(8.2)	5.3	4.1
Distributions paid	(102.2)	(102.2)	(102.2)
Net cash used in financing activities	(245.6)	(207.6)	(238.6)
Increase (decrease) in cash and cash equivalents	36.2	(0.8)	0.1
Cash and cash equivalents at beginning of period	2.9	3.7	3.6
Cash and cash equivalents at end of period	$ 39.1	$ 2.9	$ 3.7