Discontinued Operations - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended			9 Months Ended	3 Months Ended				9 Months Ended		12 Months Ended		9 Months Ended		12 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2013	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Energy Commodity [Member]	Sep. 30, 2013 Discontinued Operations [Member]	Jun. 30, 2013 Discontinued Operations [Member]	Mar. 31, 2013 Discontinued Operations [Member]	Sep. 30, 2012 Discontinued Operations [Member]	Sep. 30, 2013 Discontinued Operations [Member]	Sep. 30, 2012 Discontinued Operations [Member]	Dec. 30, 2012 Discontinued Operations [Member]	Dec. 31, 2012 Discontinued Operations [Member]	Sep. 30, 2013 Discontinued Operations [Member] Interest Expense [Member]	Sep. 30, 2013 Discontinued Operations [Member] PHI [Member] Investment	Dec. 31, 2012 Discontinued Operations [Member] PHI [Member] Investment	Sep. 30, 2013 Discontinued Operations [Member] Phi [Member]	Jun. 30, 2013 Discontinued Operations [Member] Phi [Member]	Sep. 30, 2013 Discontinued Operations [Member] Phi [Member]	Sep. 30, 2013 Discontinued Operations [Member] Phi [Member] Proceeds From Early Termination [Member]	Sep. 30, 2013 Discontinued Operations [Member] Phi [Member] Payment Paid From Early Termination [Member]	Sep. 30, 2013 Discontinued Operations [Member] Power Delivery [Member]	Sep. 30, 2013 Discontinued Operations [Member] Other Non-Regulated [Member]	Sep. 30, 2013 Discontinued Operations [Member] Corporate and Other [Member]
Derivative [Line Items]
Lease investments				$ 1,237											$ 0	$ 1,237
Number of investment in lease portfolio															0	6
Aggregate of net cash proceeds (payments) of lease investments																				873	2,000
Net pre tax gain / loss																			3
Loss on early termination of finance leases held in trust, after tax																			2
Early termination agreement of leases																	Six remaining lease investments	Six remaining lease investments
After-tax non-cash charges	377						6	323
Other non-cash charge										373
After-tax effect of revised lease rerun										313
After-tax non-cash charge														16					70
Interest benefit																						12
Interest expense on uncertain tax positions																							16	66
Maximum percentage of penalty on the amount of additional taxes due										20.00%
Expected gain upon closing of contract										3
Pre-tax loss associated with the terminations of the retail electric customer supply and wholesale purchase obligations										2
After-tax loss associated with the terminations of the retail electric customer supply and wholesale purchase obligations										8
Expected gain upon closing of contract, after tax										5
Unrealized derivative losses after tax								2
Pre-tax unrealized derivative losses								4
Net accounts receivable						0				0			33
Inventory assets		169		153		2				2			3
Gross derivative assets						0				0			1
Other current assets		74		81		0				0			1
Accrued liabilities						3				3			20
Other current liabilities		263		272		0				0			1
Gross derivative liabilities		14				0				0			21
Derivatives						0				0
Amount of net pre-tax loss arising during the period included in Accumulated Other Comprehensive Loss												10
Amount of net tax loss arising during the period included in Accumulated Other Comprehensive Loss												6
Pre-tax loss reclassified into Income from Discontinued operations, Before Taxes						0			6	10	31
Net of tax loss reclassified into Income from Discontinued operations, Net of Income Taxes									4	6	18
Accumulated Other Comprehensive Loss After-tax		9	10		11
Portion Expected to be Reclassified to Income during the Next 12 Months		1	1		10
Outstanding commodity forward contracts or derivative positions						$ 0				$ 0