Financing Receivables (Narrative) (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2019
Schedule of Financial Receivables [Line Items]
Residual Value impairment	$ 58.0
Lease investment with non-investment grade counterparties, gross	237.0
Lease investment with non-investment grade counterparties, net of deferred taxes	(27.0)
Cash Proceeds for Keystone and Conemaugh lease ownership transfer	31.5
REMA Funded credit support	$ 36.0
Powerton Station [Member]
Schedule of Financial Receivables [Line Items]
Counterparties’ S&P Credit Ratings	BB
Subsequent Event [Member]
Schedule of Financial Receivables [Line Items]
Expected tax payment for REMA restructuring		$ 85.0