Derivative Instruments and Hedging Activities (Risk Disclosures) (Details)	1 Months Ended	3 Months Ended			9 Months Ended							9 Months Ended		9 Months Ended
	Jul. 31, 2012 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2011 USD ($)	Jun. 30, 2011 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2011 USD ($)	Sep. 30, 2012 GBP (£)	Dec. 31, 2011 USD ($)	Dec. 31, 2011 GBP (£)	Sep. 30, 2012 WPD [Member] USD ($)	Sep. 30, 2012 WPD [Member] GBP (£)	Sep. 30, 2012 LG And E And KU Energy LLC [Member] USD ($)	Dec. 31, 2011 LG And E And KU Energy LLC [Member] USD ($)	Sep. 30, 2012 Louisville Gas And Electric Co [Member] USD ($)	Dec. 31, 2011 Louisville Gas And Electric Co [Member] USD ($)
Interest Rate Risk - Cash Flow Hedges (Numeric) [Abstract]
Year of expiration of the maximum maturity date of interest rate cash flow hedge contracts					2024
Notional value of interest rate cash flow hedge contracts (excludes cross-currency contracts)		$ 618,000,000			$ 618,000,000					$ 318,000,000	£ 200,000,000
Net notional value of cross-currency cash flow hedge contracts		1,300,000,000			1,300,000,000
Latest maturity date of cross-currency cash flow hedge contracts		2028			2028
Insignificant or no hedge ineffectiveness associated with interest rate cash flow hedges		insignificant	insignificant		insignificant
Hedge ineffectiveness associated with interest rate cash flow hedges						(9,000,000)
Hedge ineffectiveness associated with certain interest rate swaps that failed hedge effectiveness testing				(4,000,000)
No or insignificant after-tax gains (losses) previously recorded in AOCI reclassified to earnings related to interest rate cash flow hedge contracts		no such reclassifications	no such reclassifications		no such reclassifications	no such reclassifications
Net unrealized after-tax gains (losses) on interest rate cash flow hedge contracts expected to be reclassified into earnings during next 12 months		(13,000,000)			(13,000,000)
Interest Rate Risk - Fair Value Hedges (Numeric) [Abstract]
Year of expiration of the maximum maturity date of interest rate fair value hedge contracts	2047
Notional value of interest rate fair value hedges	99,000,000
No or insignificant hedge ineffectiveness associated with interest rate fair value hedges		did not recognize	did not recognize		did not recognize	did not recognize
No or insignificant gains (losses) associated with interest rate fair value hedges being excluded from the assessment of hedge effectiveness		did not recognize	did not recognize		did not recognize	did not recognize
No or insignificant gain (loss) resulting from firm commitments that no longer qualified as interest rate fair value hedges		did not recognize	did not recognize		did not recognize	did not recognize
Principal amount of debt related to discontinuance of fair value hedge						400,000,000
Interest rate on debt related to discontinuance of fair value hedge						7.125%
Gain (loss) resulting from firm commitments no longer qualifying as interest rate fair value hedges, pre-tax			22,000,000			22,000,000
Gain (loss) resulting from firm commitments that no longer qualified as interest rate fair value hedges			14,000,000			14,000,000
Interest Rate Risk - Economic Activity (Numeric) [Abstract]
Notional amount of interest rate swaps classified as economic activity		179,000,000			179,000,000							179,000,000		179,000,000
Year of expiration of the maximum maturity date of interest rate economic activity contracts					2033							2033		2033
The fair value, net (asset) or liability, of interest rate swap contracts classified as economic activity		62,000,000			62,000,000			60,000,000				62,000,000	60,000,000	62,000,000	60,000,000
Foreign Currency Risk - Net Investment Hedges (Numeric) [Abstract]
Notional amount of net investment hedge contracts		263,000,000			263,000,000		163,000,000
Earliest settlement date of net investment hedge contracts					December 2012
Latest settlement date of net investment hedge contracts					November 2013
Insignificant fair value of position of net investment hedge contracts					insignificant
Fair value of net asset position of net investment hedge contracts								7,000,000
Notional amount outstanding on intercompany loan qualified as a net investment hedge		100,000,000			100,000,000		62,000,000
Insignificant or no net after tax gains (losses) on net investment hedges recognized in the foreign currency translation adjustment component of AOCI		insignificant	insignificant		insignificant	insignificant
Net after tax gains (losses) on net investment hedges included in the foreign currency translation adjustment component of AOCI		15,000,000			15,000,000			19,000,000
Foreign Currency Risk - Economic Activity (Numeric) [Abstract]
Total exposure hedged related to foreign currency contracts for anticipated earnings hedges classified as economic activity		1,900,000,000			1,900,000,000		1,200,000,000		288,000,000
Fair value of net asset or (liability) position of foreign currency contracts for anticipated earnings hedges classified as economic activity		(35,000,000)			(35,000,000)			11,000,000
Earliest termination date of foreign currency contracts for anticipated earnings hedges classified as economic activity					October 2012
Latest termination date of foreign currency contracts for anticipated earnings hedges classified as economic activity					November 2014
Gains (losses) on foreign currency contracts for anticipated earnings hedges classified as economic activity		(47,000,000)	11,000,000		(40,000,000)	11,000,000
Gains (losses) on foreign currency contracts related to debt or commitments hedged with foreign currency contracts classified as economic activity						$ 55,000,000
Insignificant or no gains (losses) on foreign currency contracts related to debt or commitments hedged with foreign currency contracts classified as economic activity			insignificant