Summary of Significant Accounting Policies Summary of Significant Accounting Policies - SPPC - New Accounting Pronouncements (Details) $ in Millions	Dec. 31, 2014 USD ($)
Accounting Standards Update 2015-17 [Member] | Other Current Assets [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	$ 291
Sierra Pacific Power Company [Member] | Accounting Standards Update 2015-17 [Member] | Other Current Assets [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	42
Sierra Pacific Power Company [Member] | Accounting Standards Update 2015-17 [Member] | Other Noncurrent Liabilities [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	42
Sierra Pacific Power Company [Member] | Accounting Standards Update 2015-03 [Member] | Other Noncurrent Assets [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	10
Sierra Pacific Power Company [Member] | Accounting Standards Update 2015-03 [Member] | Other Noncurrent Liabilities [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	$ 10