The expense charged against earnings during the period to allocate the capitalized costs of regulatory assets over the periods expected to benefit from such costs.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 28

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.3)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

Name:	us-gaap_AmortizationOfRegulatoryAsset
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Employee Benefit Obligations (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
Employee Benefit Obligations (Details) (USD $) In Millions	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Pre-tax employer contributions to employee savings plan	$ 18	$ 18	$ 68	$ 67
Duke Energy Ohio [Member] \| Qualified Pension Plans [Member]
Regulatory asset amortization			5	2
Duke Energy Ohio [Member] \| Other Post-Retirement Benefit Plans [Member]
Regulatory asset amortization	1			6
Qualified Pension Plans [Member]
Regulatory asset amortization		4
Other Post-Retirement Benefit Plans [Member]
Regulatory asset amortization				$ 2