VIEs (Details) $ in Millions	Dec. 31, 2019 USD ($) MW	Dec. 31, 2018 USD ($) MW
Independent Power Producing Entities
Purchased Power Agreements [Abstract]
Generating capacity (in MW) | MW	3,986	3,770
Low-Income Housing Limited Partnerships
Amount Reflected in Consolidated Balance Sheets [Abstract]
Current assets	$ 7	$ 5
Property, plant and equipment, net	41	42
Other noncurrent assets	1	1
Total assets	49	48
Current liabilities	8	7
Mortgages and other long-term debt payable	26	26
Other noncurrent liabilities	0	0
Total liabilities	$ 34	$ 33