Statements of Cash Flows Parenthetical - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Payments To Fund Decommissioning Fund	$ 3.8	$ 4.5	$ 4.5

The cash outflow for the purchase of investments that will be held in a decommissioning trust fund.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585

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