Regulatory Matters - SPPC - Regulatory Assets (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Regulatory Assets [Line Items]
Total regulatory assets		$ 4,285	$ 4,253
Regulatory assets		130	253
Regulatory assets		4,155	4,000
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided		2,300	2,600
Employee benefit plans [Member]
Regulatory Assets [Line Items]
Total regulatory assets	[1]	778	747
Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Total regulatory assets	[2]	1,577	1,468
Abandoned Projects [Member]
Regulatory Assets [Line Items]
Total regulatory assets		136	159
Regulatory assets other [Member]
Regulatory Assets [Line Items]
Total regulatory assets		706	688
Sierra Pacific Power Company [Member]
Regulatory Assets [Line Items]
Total regulatory assets		432	476
Regulatory assets		0	32
Regulatory assets		432	444
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided		$ 254	269
Sierra Pacific Power Company [Member] | Employee benefit plans [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period	[3]	10 years
Total regulatory assets	[3]	$ 126	115
Sierra Pacific Power Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period	[4]	28 years
Total regulatory assets	[4]	$ 90	94
Sierra Pacific Power Company [Member] | Acquisition-related Costs [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		31 years
Total regulatory assets		$ 83	87
Sierra Pacific Power Company [Member] | Abandoned Projects [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		9 years
Total regulatory assets		$ 44	51
Sierra Pacific Power Company [Member] | Deferred Excess Energy Costs [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		2 years
Total regulatory assets		$ 0	32
Sierra Pacific Power Company [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets [Line Items]
Regulatory Asset, Amortization Period		17 years
Total regulatory assets		$ 22	24
Sierra Pacific Power Company [Member] | Regulatory assets other [Member]
Regulatory Assets [Line Items]
Total regulatory assets		$ 67	$ 73

[1] Represents amounts not yet recognized as a component of net periodic benefit cost that are expected to be included in regulated rates when recognized.

[2] Amounts primarily represent income tax benefits related to state accelerated tax depreciation and certain property-related basis differences that were previously flowed through to customers and will be included in regulated rates when the temporary differences reverse.

[3] Represents amounts not yet recognized as a component of net periodic benefit cost that are expected to be included in regulated rates when recognized.

[4] Amounts represent income tax benefits related to accelerated tax depreciation and certain property-related basis differences that were previously flowed through to customers and will be included in regulated rates when the temporary differences reverse.