Financing Receivables (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Number of Coal Generation Facilities Leased to GenOn REMA	3
Partial Rental Payment	$ 4
NRG commitment to invest	350
Energy Holdings [Member]
Lease investment with non-investment grade counterparties, gross	562
Lease investment with non-investment grade counterparties, net of deferred taxes	$ 23