Regulatory Matters - NPC - Other (Details) - Nevada Power Company [Member] - Public Utilities Commission, Nevada [Member] - USD ($) $ in Millions	1 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Public Utilities, General Disclosures [Line Items]
Total impact fee		$ 97
Regulatory Liabilities	$ 2
Energy Efficiency Rate Case [Member]
Public Utilities, General Disclosures [Line Items]
Customer Refund Liability, Current	$ 10		$ 18