Financing Receivables (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	0 Months Ended	3 Months Ended	9 Months Ended		0 Months Ended	3 Months Ended
	Dec. 13, 2011	Jun. 30, 2012	Sep. 30, 2012 Plant	Sep. 30, 2012 Energy Holdings [Member]	Oct. 02, 2012 Subsequent Event [Member]	Dec. 31, 2012 Subsequent Event [Member]
Lease investment with non-investment grade counterparties, gross				$ 555
Lease investment with non-investment grade counterparties, net of deferred taxes				40
Cash payment of lease	7.5
Claim payable	110
Write off of gross lease investment			264
Number of plants			2
Cash received for reimbursement of legal costs		5.2
Total recovery of Energy Holdings' indirect subsidiary companies from Dynegy leases					63
Remaining recovery recorded in Operating Revenues in the fourth quarter 2012						$ 49.9