Derivative Instruments And Hedging Activities (Cash Flow Hedges Included In Accumulated Other Comprehensive Loss) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated Other Comprehensive Loss After-tax	$ 16		$ 39
2011 Portion Expected to be Reclassified to Income during the Next 12 Months	6		24
Energy Commodity [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated Other Comprehensive Loss After-tax	6	[1]	29	[1]
2011 Portion Expected to be Reclassified to Income during the Next 12 Months	5	[1]	23	[1]
Maximum Term	17 months	[1]	29 months	[1]
Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated Other Comprehensive Loss After-tax	10		10
2011 Portion Expected to be Reclassified to Income during the Next 12 Months	$ 1		$ 1
Maximum Term	236 months		248 months

[1] The unrealized derivative losses recorded in AOCL relate to forecasted physical natural gas and electricity purchases which are used to supply retail natural gas and 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 and the purchase cost is not recognized until the period of distribution.