Long-term Debt Schedule of Long Term Debt Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
First mortgage Bonds - minimum rate	2.51%
First Mortgage Bonds, rates range from 2.51% to 9.31%, with a weighted average rate of 4.63% in 2019 and 5.01% in 2018, due at various dates through 2050	$ 2,510		$ 2,390
Pollution Control Revenue Bonds, 5% rate, due 2033	119		119
Pollution Control Revenue Bonds owned by PGE	(21)		(21)
Total long-term debt	2,608		2,488
Debt Instrument, Unamortized Discount	(11)		(10)
Less: current portion of long-term debt	0	$ (50)	(300)
Long-term debt, net of current portion	$ 2,597		$ 2,178
First Mortgage Bonds - maximum rate	9.31%
Debt, Weighted Average Interest Rate	4.63%