Financing Receivables (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Sep. 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					$ 337
Lease investment with non-investment grade counterparties, net of deferred taxes					$ (184)
Powerton Station [Member]
Schedule of Financial Receivables [Line Items]
Counterparties’ S&P Credit Ratings					BB-