Business Segments (Details)		2 Months Ended
		Dec. 31, 2016 USD ($) segment	Dec. 31, 2015 USD ($)	Oct. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | segment		1
Segment Reporting Information [Abstract]
Total Assets		$ 5,944,100,000		$ 5,691,000,000
Segment Reporting Information, Profit (Loss) [Abstract]
Unaffiliated revenues		308,200,000
Related party revenue from Duke Energy	[1]	13,500,000
Total operating revenues		321,700,000	$ 259,600,000
Segment income (loss)		54,100,000	52,000,000
Gas Utilities and Infrastructure
Segment Reporting Information [Abstract]
Total Assets		5,944,100,000
Segment Reporting Information, Profit (Loss) [Abstract]
Unaffiliated revenues		308,200,000
Related party revenue from Duke Energy		13,500,000
Total operating revenues		321,700,000	259,600,000
Segment income (loss)		59,200,000	57,100,000
Other Segments
Segment Reporting Information [Abstract]
Total Assets		0
Segment Reporting Information, Profit (Loss) [Abstract]
Unaffiliated revenues		0
Related party revenue from Duke Energy		0
Total operating revenues		0	0
Segment income (loss)		$ (5,100,000)	$ (5,100,000)

[1] See Note 9 for details on related party transactions with Duke Energy.