Acquisitions, Discontinued Operations and Dispositions - Acquisitions (Details) customer in Thousands, $ in Millions				1 Months Ended	12 Months Ended
	Jan. 05, 2021 USD ($) customer state	Sep. 29, 2020 USD ($)	Aug. 01, 2019 USD ($) customer state	Dec. 31, 2020 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jan. 05, 2021 province
Business Acquisition [Line Items]
Number of states in which the entity operates | state			9
Acquisition costs					$ 25
Revenues					26,989	$ 9,093	$ 9,821
Income from continuing operations before income taxes					2,859	761	786
Operating lease liability					317
Joliet facility
Business Acquisition [Line Items]
Lease expense							$ 14
Operating lease liability		$ 148
Powerton Facility And Units 7 And 8 Of The Joliet Facility
Business Acquisition [Line Items]
Purchase of assets		$ 260
Direct Energy
Business Acquisition [Line Items]
Customers added (over) | customer	3,000
Purchase price	$ 3,625
Purchase price adjustment	77				22
Cash paid to acquire business	715
Proceeds from revolving credit facility	166
Acquisition costs	$ 107					$ 17
Proceeds from issuance of secured and unsecured corporate debt				$ 2,900
Revenues					15,600
Income from continuing operations before income taxes					$ 2,400
Direct Energy | Customer Relationships
Business Acquisition [Line Items]
Intangible assets, useful life	12 years
Direct Energy | Customer and Supply Contracts
Business Acquisition [Line Items]
Intangible assets, useful life	14 years
Direct Energy | Trade Names
Business Acquisition [Line Items]
Intangible assets, useful life	15 years
Direct Energy | U.S.
Business Acquisition [Line Items]
Number of states in which the entity operates | state	50
Direct Energy | Canada
Business Acquisition [Line Items]
Provinces in which entity operates	8							8
Stream Energy
Business Acquisition [Line Items]
Cash paid to acquire business			$ 329
Working capital adjustments			$ 29
Residential customer equivalents acquired | customer			600
Customers acquired | customer			450