Financing Receivables (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Schedule of Financial Receivables [Line Items]
Pre-Tax Lease write-down	$ 58
Lease investment with non-investment grade counterparties, gross		$ 235
Lease investment with non-investment grade counterparties, net of deferred taxes		(25)
Assets to be classified as Held-for-sale		$ 29		$ 30
Powerton Station [Member]
Schedule of Financial Receivables [Line Items]
Counterparties’ S&P Credit Ratings		BB
Subsequent Event [Member]
Schedule of Financial Receivables [Line Items]
Assets to be classified as Held-for-sale			$ 160