Financing Receivables (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016
Schedule of Financial Receivables [Line Items]
Pre-tax write down/charge against lease receivables	$ 55	$ 10	$ 137
Lease investment with non-investment grade counterparties, gross	371
Lease investment with non-investment grade counterparties, net of deferred taxes	$ (154)
Powerton Station [Member]
Schedule of Financial Receivables [Line Items]
Counterparties’ S&P Credit Ratings	BB-