Risk Management and Hedging Activities - NPC - Balance Sheet Location (Details) - Commodity derivative [Member] - USD ($) $ in Millions		Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016		Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Net Regulatory Asset (Liability), Unrealized Loss (Gain) On Derivative Contracts		$ 162	$ 162	$ 148		$ 195	$ 185	$ 250
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		196		206
Not Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		60		46
Not Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		135		150
Nevada Power Company [Member] | Not Designated as Hedging Instrument [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	[1]	3		7
Nevada Power Company [Member] | Not Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	[1]	1		7
Recurring [Member] | Nevada Power Company [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		4		14
Recurring [Member] | Level 3 [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		16		27
Recurring [Member] | Level 3 [Member] | Nevada Power Company [Member]
Derivatives, Fair Value [Line Items]
Net Regulatory Asset (Liability), Unrealized Loss (Gain) On Derivative Contracts		4		14	[1]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	[1]	$ 4		$ 14

[1] (1)Nevada Power's commodity derivatives not designated as hedging contracts are included in regulated rates and as of September 30, 2017 and December 31, 2016, a regulatory asset of $4 million and $14 million, respectively, was recorded related to the derivative liability of $4 million and $14 million, respectively.