Derivative Instruments And Hedging Activities (Cash Flow Hedges Included In Accumulated Other Comprehensive Loss) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated Other Comprehensive Loss After-tax	$ 11		$ 21
Portion Expected to be Reclassified to Income during the Next 12 Months	2		11
Energy Commodity [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated Other Comprehensive Loss After-tax	1	[1]	11	[2]
Portion Expected to be Reclassified to Income during the Next 12 Months	1	[1]	10	[2]
Maximum Term	2 months	[1]	14 months	[2]
Interest Rate [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated Other Comprehensive Loss After-tax	10		10
Portion Expected to be Reclassified to Income during the Next 12 Months	$ 1		$ 1
Maximum Term	233 months		245 months

[1] The unrealized derivative losses recorded in AOCL relate to forecasted physical electricity purchases which are used to supply retail electricity contracts that are in gain positions and subject to accrual accounting. Under accrual accounting, no asset is recorded on PHI's consolidated balance sheet for the retail contracts and the purchase cost is not recognized until the period of distribution.

[2] The unrealized derivative losses recorded in AOCL relate to forecasted physical and electricity purchases which are used to supply retail electricity contracts that are in gain positions and subject to accrual accounting. Under accrual accounting, no asset is recorded on PHI's consolidated balance sheet for the retail contracts and the purchase cost is not recognized until the period of distribution.