Basis of Presentation - Transformation Plan (Details) $ in Millions		12 Months Ended
	Jul. 12, 2017 USD ($) MW	Dec. 31, 2020 USD ($)	Jun. 30, 2017 MW
Restructuring Cost and Reserve [Line Items]
Generation capacity (in MW) | MW			31,000
Transformation Plan | Subsequent Event
Restructuring Cost and Reserve [Line Items]
Term of plan	3 years
Non-recurring working capital improvements		$ 370
Costs expected to be spent		$ 290
Transformation Plan | Subsequent Event | Operations and cost excellence
Restructuring Cost and Reserve [Line Items]
Cost savings	$ 1,065
Transformation Plan | Subsequent Event | Operations and cost excellence | Annual cost savings
Restructuring Cost and Reserve [Line Items]
Cost savings	590
Transformation Plan | Subsequent Event | Operations and cost excellence | Net margin enhancement program
Restructuring Cost and Reserve [Line Items]
Cost savings	215
Transformation Plan | Subsequent Event | Operations and cost excellence | Annual reduction in maintenance capital expenditures
Restructuring Cost and Reserve [Line Items]
Cost savings	50
Transformation Plan | Subsequent Event | Operations and cost excellence | Permanent selling general and administrative reduction associated with asset sales
Restructuring Cost and Reserve [Line Items]
Cost savings	$ 210
Transformation Plan | Subsequent Event | Portfolio optimization
Restructuring Cost and Reserve [Line Items]
Generation capacity (in MW) | MW	6,000
Transformation Plan | Subsequent Event | Portfolio optimization | Minimum
Restructuring Cost and Reserve [Line Items]
Effect on cash flows	$ 2,500
Transformation Plan | Subsequent Event | Portfolio optimization | Minimum | NRG Yield, Inc.
Restructuring Cost and Reserve [Line Items]
Ownership interest	50.00%
Transformation Plan | Subsequent Event | Portfolio optimization | Maximum
Restructuring Cost and Reserve [Line Items]
Effect on cash flows	$ 4,000
Transformation Plan | Subsequent Event | Portfolio optimization | Maximum | NRG Yield, Inc.
Restructuring Cost and Reserve [Line Items]
Ownership interest	100.00%
Transformation Plan | Subsequent Event | Capital structure and allocation enhancements
Restructuring Cost and Reserve [Line Items]
Reduction in consolidated debt, original amount	$ 19,500
Reduction in consolidated debt	18,000
Cnsolidated debt original amount reduction	6,500
Consolidated debt, net amount reduction	$ 6,000
Corporate net debt (corporate debt less cash and cash equivalents) to EBITDA ratio	3.0
Transformation Plan | Subsequent Event | Capital structure and allocation enhancements | Minimum
Restructuring Cost and Reserve [Line Items]
Effect on cash flows	$ 0
Transformation Plan | Subsequent Event | Capital structure and allocation enhancements | Maximum
Restructuring Cost and Reserve [Line Items]
Effect on cash flows	$ 6,300