Supplemental Cash Flow Disclosures - NPC (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	$ 627	$ 935
Restricted Cash and Cash Equivalents, Current	227	327
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	883	1,283	$ 1,003	$ 1,332
Interest paid, net of amounts capitalized	1,713	1,715	1,673
Accruals related to property, plant and equipment additions	823	653	547
Nevada Power Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	111	57
Restricted Cash and Cash Equivalents, Current	10	9
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	121	66	290	$ 547
Interest paid, net of amounts capitalized	166	167	173
Income Taxes Paid	117	89	0
Accruals related to property, plant and equipment additions	34	18	19
Capital and Financial Lease Obligations Incurred	$ 1	$ 0	$ (1)