Segment Information (Schedule of Other Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Segment Reporting Information [Line Items]
Cash and cash equivalents	$ 4	$ 13
Property, plant and equipment	4,284	4,111
Unamortized debt expense	18	20
Right-of-use lease assets	155	163
TOTAL ASSETS	5,247	$ 5,160	$ 5,275
Other
Segment Reporting Information [Line Items]
Cash and cash equivalents	4		5
Income taxes receivable	0		32
Prepayments	6		9
Property, plant and equipment	15		23
Unamortized debt expense	11		10
Right-of-use lease assets	70		77
Non-qualified retirement plan	4		5
TOTAL ASSETS	$ 110		$ 161