Statements Of Consolidated Common Stockholders' Equity (Parenthetical) (USD $) In Millions, unless otherwise specified	0 Months Ended	3 Months Ended
Feb. 11, 2015	Mar. 31, 2015
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest	15.70%	8.40%
Proceeds from Issuance Initial Public Offering	$ 1,168.4

The cash inflow associated with the amount received from entity's first offering of stock to the public.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3255-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration