Long-term Debt Schedule of Long Term Debt Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
First Mortgage Bonds, rates range from 2.51% to 9.31%, with a weighted average rate of 5.03% in 2017 and 4.86% in 2016, due at various dates through 2048	$ 2,315	$ 2,090
Unsecured term bank loans, variable rates of approximately 1.87% at 11/27/2017 and 1.37% at 12/31/2016	0	150
Pollution Control Revenue Bonds, 5% rate, due 2033	142	142
Pollution Control Revenue Bonds owned by PGE	(21)	(21)
Debt Instrument, Unamortized Discount	(10)	(11)
Total long-term debt	2,436	2,361
Less: current portion of long-term debt	0	(150)
Long-term debt, net of current portion	$ 2,426	$ 2,200