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Risk Management Activities (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2017 | Mar. 31, 2016 | Apr. 03, 2017 | Dec. 31, 2016
Derivative [Line Items] |  |  |  |
Notional Amount of Forward-Starting Interest rate Swap Agreements |  |  |  | $ 1,500.0
Risk management assets |  |  |  |
Derivative [Line Items] |  |  |  |
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net | $ 0.0 | $ 0.0 |  |
Subsequent Event |  |  |  |
Derivative [Line Items] |  |  |  |
Notional Amount of Forward-Starting Interest rate Swap Agreements |  |  | $ 200.0 |

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- Definition The net gain (loss) recognized in earnings during the reporting period representing the amount of the cash flow hedges' ineffectiveness. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624171-113959 + Details
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