Financing Receivables (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2017
Schedule of Financial Receivables [Line Items]
Lease Receivable adjustment	$ 15	$ 55	$ 10
Residual Value Adjustment	7			$ 137
Lease investment with non-investment grade counterparties, gross	348				$ 348
Lease investment with non-investment grade counterparties, net of deferred taxes	$ (159)				$ (159)
Powerton Station [Member]
Schedule of Financial Receivables [Line Items]
Counterparties’ S&P Credit Ratings					BB-