Use of Collateral (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Financial Instruments Owned and Pledged as Collateral [Line Items]
Margin Deposit Assets	[1]	$ 432	$ 343
Natural gas and power prepayments		29	31
Total margin deposits and natural gas and power prepayments with our counterparties	[2]	461	374
Letters of credit issued		906	1,166
First priority liens under power and natural gas agreements		42	92
First priority liens under interest rate hedging instruments		31	10
Letters of Credit Issued and First Priority Liens Under Power Natural Gas And Interest Rate Hedging Instruments		979	1,268
Margin deposits posted with us by our counterparties	[1],[3]	127	52
Letters of credit posted with us by our counterparties		25	27
Total margin deposits and letters of credit posted with us by our counterparties		152	79
Prepaid Expenses and Other Current Assets [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total margin deposits and natural gas and power prepayments with our counterparties		336	286
Other Assets [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total margin deposits and natural gas and power prepayments with our counterparties		8	9
Current and Non-current Derivative Assets and Liabilities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total margin deposits and natural gas and power prepayments with our counterparties		117	79
Margin deposits posted with us by our counterparties		3	32
Other Current Liabilities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Margin deposits posted with us by our counterparties		93	20
Other Noncurrent Liabilities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Margin deposits posted with us by our counterparties		$ 31	$ 0

[1] We offset fair value amounts recognized for derivative instruments executed with the same counterparty under a master netting arrangement for financial statement presentation; therefore, amounts recognized for the right to reclaim, or the obligation to return, cash collateral are presented net with the corresponding derivative instrument fair values. See Note 10 for further discussion of our derivative instruments subject to master netting arrangements.

[2] At December 31, 2019 and 2018, $117 million and $79 million, respectively, were included in current and long-term derivative assets and liabilities, $336 million and $286 million, respectively, were included in margin deposits and other prepaid expense and $8 million and $9 million, respectively, were included in other assets on our Consolidated Balance Sheets.

[3] At December 31, 2019 and 2018, $3 million and $32 million, respectively, were included in current and long-term derivative assets and liabilities, $93 million and $20 million, respectively, were included in other current liabilities and $31 million and nil, respectively, were included in other long-term liabilities on our Consolidated Balance Sheets.