Summary of Significant Accounting Policies and Other Matters - Long-Lived and Intangible Assets (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) MW	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ 29,000,000	$ 15,000,000
Amortization of intangible assets	14,000,000	9,000,000	$ 2,000,000
Amortization expense, 2019	105,000,000
Amortization expense, 2020	105,000,000
Amortization expense, 2021	105,000,000
Amortization expense, 2022	105,000,000
Amortization expense, 2023	105,000,000
Asset impairment	2,000,000
Impairment charges on long-lived assets		0	0
Impairment charges on intangible assets		0	$ 0
Long-term debt	18,145,000,000	16,029,000,000
Net non-utility plant	41,749,000,000	37,600,000,000
Intangible assets	1,654,000,000	131,000,000
PG&E Project
Finite-Lived Intangible Assets [Line Items]
Long-term debt	1,050,000,000
Net non-utility plant	885,000,000
Intangible assets	$ 1,125,000,000
PG&E Project | Con Edison Development
Finite-Lived Intangible Assets [Line Items]
Aggregate power to be sold (in MW) | MW	680
PG&E Project | Secured Related to Project Debt
Finite-Lived Intangible Assets [Line Items]
Net non-utility plant	$ 292,000,000
Other Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net	3,000,000
Accumulated amortization	7,000,000	6,000,000
Power Purchase Agreements
Finite-Lived Intangible Assets [Line Items]
Intangible assets, net	1,712,000,000	131,000,000
Accumulated amortization	$ 22,000,000	$ 9,000,000