Assets Held for Sale Assets Held for Sale (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	9 Months Ended
Jan. 31, 2014	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Assets held for sale		$ 0		$ 36.2
Proceeds from sale of assets	37.7	37.7	0
Kansas City Power and Light Company [Member]
Assets held for sale		0		4.7
Proceeds from sale of assets	$ 4.7	$ 4.7	$ 0

The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 12

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585

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