Financing Receivables (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of Financial Receivables [Line Items]
Lease Receivable adjustment	$ 20	$ 22	$ 55	$ 20	$ 77
Provision for Loan and Lease Losses		$ 7
Lease investment with non-investment grade counterparties, gross	315			315
Lease investment with non-investment grade counterparties, net of deferred taxes	$ (112)			$ (112)
Powerton Station [Member]
Schedule of Financial Receivables [Line Items]
Counterparties’ S&P Credit Ratings				BB-