Regulatory Matters Regulatory Matters - NPC - 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
Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years	[1]	26 years
Total regulatory assets	[1]	$ 1,577	1,468
Employee benefit plans [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years	[2]	9 years
Total regulatory assets	[2]	$ 778	747
Abandoned Projects [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years		5 years
Total regulatory assets		$ 136	159
Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years		8 years
Total regulatory assets		$ 281	239
Regulatory assets other [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years		Various
Total regulatory assets		$ 706	688
Nevada Power Company [Member]
Regulatory Assets [Line Items]
Total regulatory assets		1,057	1,126
Regulatory assets		0	57
Regulatory assets		1,057	1,069
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided		$ 572	788
Nevada Power Company [Member] | Deferred Income Tax Charge [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years	[3]	P28Y
Total regulatory assets	[3]	$ 149	156
Nevada Power Company [Member] | Acquisition-related Costs [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years		P28Y
Total regulatory assets		$ 143	149
Nevada Power Company [Member] | Decommissioning costs [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years		P7Y
Total regulatory assets		$ 121	113
Nevada Power Company [Member] | Employee benefit plans [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years	[4]	P10Y
Total regulatory assets	[4]	$ 98	85
Nevada Power Company [Member] | Abandoned Projects [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years		P4Y
Total regulatory assets		$ 91	107
Nevada Power Company [Member] | Deferred Operating Costs [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years		P20Y
Total regulatory assets		$ 87	61
Nevada Power Company [Member] | Asset Retirement Obligation Costs [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years		P7Y
Total regulatory assets		$ 79	80
Nevada Power Company [Member] | Legacy Meters [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years		P17Y
Total regulatory assets		$ 64	68
Nevada Power Company [Member] | Deferred Excess Energy Costs [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years		P2Y
Total regulatory assets		$ 56	129
Nevada Power Company [Member] | Regulatory assets other [Member]
Regulatory Assets [Line Items]
Regulatory asset amortization period years		Various
Total regulatory assets		$ 169	178
Public Utilities Commission, Nevada [Member] | General Rate Case [Member] | Nevada Power Company [Member]
Regulatory Assets [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets			$ 5

[1] 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.

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

[3] 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.

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