Nature Of Operations And Summary Of Significant Accounting Policies (Narrative) (Details)
$ in Millions |
12 Months Ended |
|
Dec. 31, 2015
USD ($)
mi
|
Dec. 31, 2014
USD ($)
|
Dec. 31, 2013
USD ($)
|
| Basis Of Accounting Presentation [Line Items] |
|
|
|
| Pipeline Length | mi |
15,000
|
|
|
| Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest |
15.70%
|
|
|
| Base Gas Purchases |
$ 0.0
|
$ 0.0
|
$ 0.0
|
| Amortized software costs |
5.8
|
4.3
|
5.0
|
| Unamortized software costs |
27.1
|
18.3
|
|
| Goodwill |
1,975.5
|
|
|
| Asset Impairment Charges |
0.6
|
0.0
|
0.0
|
| Royalty Revenue |
26.5
|
43.8
|
21.2
|
| Gain on Conveyances |
52.3
|
34.5
|
$ 7.3
|
| Capitalized Exploratory Well Costs that Have Been Capitalized for Period Greater than One Year |
$ 0.3
|
|
|
| Projects that have Exploratory Well Costs that have been Capitalized for Period Greater than One Year, Number of Projects |
1
|
|
|
| Joint Ventures [Member] |
|
|
|
| Basis Of Accounting Presentation [Line Items] |
|
|
|
| Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest |
84.30%
|
|
|
| Millennium Pipeline |
|
|
|
| Basis Of Accounting Presentation [Line Items] |
|
|
|
| Equity Method Investment, Ownership Percentage |
47.50%
|
|
|
| Hardy Storage |
|
|
|
| Basis Of Accounting Presentation [Line Items] |
|
|
|
| Equity Method Investment, Ownership Percentage |
49.00%
|
|
|
| Pennant |
|
|
|
| Basis Of Accounting Presentation [Line Items] |
|
|
|
| Equity Method Investment, Initial Ownership Percentage |
5.00%
|
|
|
| Equity Method Investment, Ownership Percentage |
47.50%
|
|
|
| Cash Received from Buy-In |
$ 12.7
|
|
|
| Gain on Buy-In |
$ 2.9
|
|
|
| Maximum | Pennant |
|
|
|
| Basis Of Accounting Presentation [Line Items] |
|
|
|
| Equity Method Investment, Ownership Percentage |
33.33%
|
|
|
| Previous [Member] | Pennant |
|
|
|
| Basis Of Accounting Presentation [Line Items] |
|
|
|
| Equity Method Investment, Ownership Percentage |
50.00%
|
|
|
| Predecessor |
|
|
|
| Basis Of Accounting Presentation [Line Items] |
|
|
|
| Goodwill |
|
$ 1,975.5
|
|
| Predecessor | Hardy Storage |
|
|
|
| Basis Of Accounting Presentation [Line Items] |
|
|
|
| Equity Method Investment, Ownership Percentage |
|
50.00%
|
|