Statements Of Cash Flows Parenthetical - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014
Payments To Fund Decommissioning Fund	$ 2.3	$ 2.3

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=31042434&loc=d3e3213-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

Name:	us-gaap_PaymentsToInvestInDecommissioningFund
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration