Summary of Significant Accounting Policies Summary of Significant Accounting Policies - NPC - New Accounting Pronouncements (Details) $ in Millions	Dec. 31, 2014 USD ($)
Other Current Assets [Member] | Accounting Standards Update 2015-17 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	$ 291
Nevada Power Company [Member] | Other Current Assets [Member] | Accounting Standards Update 2015-17 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	145
Nevada Power Company [Member] | Other Noncurrent Assets [Member] | Accounting Standards Update 2015-03 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	32
Nevada Power Company [Member] | Other Noncurrent Liabilities [Member] | Accounting Standards Update 2015-17 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	145
Nevada Power Company [Member] | Other Noncurrent Liabilities [Member] | Accounting Standards Update 2015-03 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	$ 32