Assets and Liabilities with Recurring Fair Value Measurements Quantitative Info on Level 3 (Details) - USD ($)		Jun. 30, 2020	Dec. 31, 2019
Fair Value Measurements Inputs and Valuation Techniques
Derivative, fair value, net asset (liability)	[1]	$ 85,000,000	$ 114,000,000
Power Contracts
Fair Value Measurements Inputs and Valuation Techniques
Derivative, fair value, net asset (liability)	[2]	206,000,000	158,000,000
Power Contracts | Minimum [Member]
Fair Value Measurements Inputs and Valuation Techniques
Fair value inputs quantitative information		3.18	4.85
Power Contracts | Maximum
Fair Value Measurements Inputs and Valuation Techniques
Fair value inputs quantitative information		175.51	184.15
Power Contracts | Average
Fair Value Measurements Inputs and Valuation Techniques
Fair value inputs quantitative information	[3]	28.97
Power Congestion Products
Fair Value Measurements Inputs and Valuation Techniques
Derivative, fair value, net asset (liability)		6,000,000	17,000,000
Power Congestion Products | Minimum [Member]
Fair Value Measurements Inputs and Valuation Techniques
Fair value inputs quantitative information		(6.48)	(10.32)
Power Congestion Products | Maximum
Fair Value Measurements Inputs and Valuation Techniques
Fair value inputs quantitative information		11.88	20.00
Power Congestion Products | Average
Fair Value Measurements Inputs and Valuation Techniques
Fair value inputs quantitative information	[3]	1.20
Natural Gas Contracts
Fair Value Measurements Inputs and Valuation Techniques
Derivative, fair value, net asset (liability)		9,000,000	(20,000,000)
Natural Gas Contracts | Minimum [Member]
Fair Value Measurements Inputs and Valuation Techniques
Fair value inputs quantitative information		1.33	1.73
Natural Gas Contracts | Maximum
Fair Value Measurements Inputs and Valuation Techniques
Fair value inputs quantitative information		4.62	$ 6.45
Natural Gas Contracts | Average
Fair Value Measurements Inputs and Valuation Techniques
Fair value inputs quantitative information	[3]	$ 2.82

[1] At June 30, 2020 and December 31, 2019, we had $260 million and $191 million, respectively, of collateral under master netting arrangements that were not offset against our derivative instruments on the Consolidated Condensed Balance Sheets primarily related to initial margin requirements.

[2] Power contracts include power and heat rate instruments classified as level 3 in the fair value hierarchy.

[3] (2)Amount represents the arithmetic average of the significant unobservable input based on the range disclosed.