Financing Receivables (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013
Net Investments in Leases	$ 117		$ 98
Lease investment with non-investment grade counterparties, gross			561
Lease investment with non-investment grade counterparties, net of deferred taxes			7
Partial Rental Payment			4
NRG commitment to invest			350
Claim payable		110
Write off of gross lease investment		264
Remaining recovery recorded in Operating Revenues in 2012	63
Annual Rent commencing in July 2015			$ 14
Powerton Station [Member]
Lease Receivable Percent Owned			64.00%