Derivative Instruments and Hedging - Offsetting of Derivatives, Locations in Condensed Consolidated Balance Sheet and Amounts of Derivatives (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative Asset	$ 109	$ 95
Derivative Liability	(144)	(105)
Current Liabilities | Designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative liabilities	(31)	0
Networks | Current Assets
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total derivatives before offset of cash collateral, Asset	1	0
Cash collateral (payable) receivable, Asset	0	0
Total derivatives as presented in the balance sheet, Asset	1	0
Networks | Current Assets | Not designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	2	1
Derivative liabilities	(1)	(1)
Derivative Asset	1	0
Networks | Current Assets | Designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Derivative Asset	0	0
Networks | Noncurrent Assets
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total derivatives before offset of cash collateral, Asset	2	2
Cash collateral (payable) receivable, Asset	0	0
Total derivatives as presented in the balance sheet, Asset	2	2
Networks | Noncurrent Assets | Not designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	3	4
Derivative liabilities	(1)	(2)
Derivative Asset	2	2
Networks | Noncurrent Assets | Designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Derivative Asset	0	0
Networks | Current Liabilities
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total derivatives before offset of cash collateral, Liability	(45)	(39)
Cash collateral (payable) receivable, Liability	28	27
Total derivatives as presented in the balance sheet, Liability	(17)	(12)
Networks | Current Liabilities | Not designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	2	1
Derivative liabilities	(42)	(39)
Derivative Liability	(40)	(38)
Networks | Current Liabilities | Designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	0	0
Derivative liabilities	(5)	(1)
Derivative Liability	(5)	(1)
Networks | Noncurrent Liabilities
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total derivatives before offset of cash collateral, Liability	(95)	(85)
Cash collateral (payable) receivable, Liability	6	1
Total derivatives as presented in the balance sheet, Liability	(89)	(84)
Networks | Noncurrent Liabilities | Not designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	1	2
Derivative liabilities	(92)	(86)
Derivative Liability	(91)	(84)
Networks | Noncurrent Liabilities | Designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	0	0
Derivative liabilities	(4)	(1)
Derivative Liability	(4)	(1)
Renewables | Current Assets
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total derivatives before offset of cash collateral, Asset	34	22
Cash collateral (payable) receivable, Asset	(11)	(11)
Total derivatives as presented in the balance sheet, Asset	23	11
Renewables | Current Assets | Not designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	35	23
Derivative liabilities	(1)	(1)
Derivative Asset	34	22
Renewables | Current Assets | Designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Derivative Asset	0	0
Renewables | Noncurrent Assets
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total derivatives before offset of cash collateral, Asset	110	112
Cash collateral (payable) receivable, Asset	(27)	(30)
Total derivatives as presented in the balance sheet, Asset	83	82
Renewables | Noncurrent Assets | Not designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	108	110
Derivative liabilities	(2)	(7)
Derivative Asset	106	103
Renewables | Noncurrent Assets | Designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	17	18
Derivative liabilities	(13)	(9)
Derivative Asset	4	9
Renewables | Current Liabilities
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total derivatives before offset of cash collateral, Liability	(6)	(14)
Cash collateral (payable) receivable, Liability	1	7
Total derivatives as presented in the balance sheet, Liability	(5)	(7)
Renewables | Current Liabilities | Not designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	37	42
Derivative liabilities	(43)	(48)
Derivative Liability	(6)	(6)
Renewables | Current Liabilities | Designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	8	5
Derivative liabilities	(8)	(13)
Derivative Liability	0	(8)
Renewables | Noncurrent Liabilities
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total derivatives before offset of cash collateral, Liability	(3)	(7)
Cash collateral (payable) receivable, Liability	1	6
Total derivatives as presented in the balance sheet, Liability	(2)	(1)
Renewables | Noncurrent Liabilities | Not designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	17	13
Derivative liabilities	(21)	(18)
Derivative Liability	(4)	(5)
Renewables | Noncurrent Liabilities | Designated as hedging instruments
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative assets	8	4
Derivative liabilities	(7)	(6)
Derivative Liability	$ 1	$ (2)