Supplemental Cash Flow Disclosures - NPC (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Cash Flow Statements, Captions [Line Items]
Interest paid, net of amounts capitalized	$ 1,764	$ 1,585	$ 1,073
Accruals related to property, plant and equipment additions	718	1,143	661
Nevada Power Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Interest paid, net of amounts capitalized	186	194	209
Accruals related to property, plant and equipment additions	51	30	25
Capital and Financial Lease Obligations Incurred	$ (5)	$ 7	$ 419