Commitments and Contingencies - Narrative (Details) (USD $) In Millions, unless otherwise specified				3 Months Ended		12 Months Ended		3 Months Ended
	Mar. 31, 2014	Mar. 31, 2014 Subrogation Lawsuit [Member] Caughlin Fire [Member] Claims	Mar. 31, 2014 Individual Claimant [Member] Caughlin Fire [Member] Claims	Mar. 31, 2014 One Of Individual Claimants [Member] Caughlin Fire [Member] plaintiff	Dec. 17, 2013 Newmont Nevada Energy Investment, LLC [Member]	Dec. 31, 2013 Newmont Nevada Energy Investment, LLC [Member] TS Power Plant [Member] MW	Jun. 30, 2009 Valmy Generating Station [Member] Idaho Power Company [Member]	Mar. 31, 2014 ON Line Transmission Line [Member] Nevada Power Company [Member]	Mar. 31, 2014 ON Line Transmission Line [Member] Sierra Pacific Power Company [Member]
Loss Contingencies [Line Items]
Company share							50.00%
Coal-fired power plant capacity						203
Amount of bond posted					$ 1
Subsynchronous resonance costs	1
Installation costs of protection equipment	$ 11
Utilities Aggregate Share Transmission Line Project								95.00%	5.00%
Number of lawsuits		6	2
Loss Contingency, Number of Plaintiffs				6