Fair Value Measurements - NPC (Details) - Recurring [Member] - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		$ 3,917	$ 3,114
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		2,649	2,423
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		1,167	625
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		126	118
Money market mutual funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI		837	409
Money market mutual funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI		837	409
Money market mutual funds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI		0	0
Money market mutual funds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI		0	0
Investment funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI		182	128
Investment funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI		182	128
Investment funds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI		0	0
Investment funds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI		0	0
Commodity derivative [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement		0	1
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		(3)	(1)
Commodity derivative [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement		36	91
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		(142)	(180)
Commodity derivative [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement		103	108
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		(25)	(9)
Nevada Power Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		263	112
Nevada Power Company [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		263	105
Nevada Power Company [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		0	0
Nevada Power Company [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		0	7
Nevada Power Company [Member] | Money market mutual funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI	[1]	261	104
Nevada Power Company [Member] | Money market mutual funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI	[1]	261	104
Nevada Power Company [Member] | Money market mutual funds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI	[1]	0	0
Nevada Power Company [Member] | Money market mutual funds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI	[1]	0	0
Nevada Power Company [Member] | Investment funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI		2	1
Nevada Power Company [Member] | Investment funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI		2	1
Nevada Power Company [Member] | Investment funds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI		0	0
Nevada Power Company [Member] | Investment funds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity Securities, FV-NI		0	0
Nevada Power Company [Member] | Commodity derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement			7
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		(18)	(4)
Nevada Power Company [Member] | Commodity derivative [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement			0
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		0	0
Nevada Power Company [Member] | Commodity derivative [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement			0
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		0	0
Nevada Power Company [Member] | Commodity derivative [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative asset, fair value, gross asset including not subject to master netting arrangement			7
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		$ (18)	$ (4)

[1] Amounts are included in cash and cash equivalents on the Consolidated Balance Sheets. The fair value of these money market mutual funds approximates cost.