Variable Interest Entities (Detail) $ in Millions			9 Months Ended
	May 08, 2020 USD ($) wind_farm MW	Mar. 02, 2020 USD ($) numberOfInvestors wind_farm agreement	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Variable Interest Entity [Line Items]
Number of TEF agreements | agreement		2
Contributions from noncontrolling interests	$ 70	$ 237	$ 312	$ 133
Number of tax equity investors | numberOfInvestors		2
Wind firms that reached commercial operation | wind_farm	3	2
Wind farms expected to be part of Aeolus VII | wind_farm	4
Proposed wind farm and electricity transmission project capacity (MW) | MW	681
Assets of variable interest entities (VIEs)			35,640		$ 34,416
Liabilities of variable interest entities (VIEs)			19,786		18,830
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Assets of variable interest entities (VIEs)			1,720		806
Liabilities of variable interest entities (VIEs)			$ 104		$ 29