Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 227us-gaap_NetIncomeLoss	$ 145us-gaap_NetIncomeLoss	$ 258us-gaap_NetIncomeLoss
Adjustments to reconcile net income to net cash from operating activities:
Loss on nonrecurring items	15us-gaap_OtherNonrecurringIncomeExpense	0us-gaap_OtherNonrecurringIncomeExpense	(4)us-gaap_OtherNonrecurringIncomeExpense
Depreciation and amortization	274	277	270
Deferred income taxes and amortization of investment tax credits	130	95	151
Allowance for equity funds	(1)	(8)	(7)
Amortization of deferred charges	79us-gaap_AmortizationOfDeferredCharges	(54)us-gaap_AmortizationOfDeferredCharges	(170)us-gaap_AmortizationOfDeferredCharges
Deferred Energy Charge	(44)npc_DeferredEnergyChange	(105)npc_DeferredEnergyChange	112npc_DeferredEnergyChange
Amortization of other regulatory asset	47us-gaap_AmortizationOfRegulatoryAsset	89us-gaap_AmortizationOfRegulatoryAsset	88us-gaap_AmortizationOfRegulatoryAsset
Other, net	72us-gaap_OtherNoncashIncomeExpense	90us-gaap_OtherNoncashIncomeExpense	(25)us-gaap_OtherNoncashIncomeExpense
Accounts receivable and other assets
Accounts receivable and other assets	(71)	(12)	3
Inventories	(15)us-gaap_IncreaseDecreaseInInventories	10us-gaap_IncreaseDecreaseInInventories	(5)us-gaap_IncreaseDecreaseInInventories
Accounts payable and other liabilities	(9)	21	31
Net cash flows from operating activities	704	548	702
Cash flows from investing activities:
Capital expenditures	(410)	(267)	(288)
Proceeds from contribution in aid of construction and customer advances	39	34	43
Proceeds from sale of asset	0	14	0
Other, net	0	3	0
Net cash flows from investing activities	(371)	(216)	(245)
Cash flows from financing activities:
Proceeds from issuance of long-term debt, net of costs	0	0	132
Repayments of long-term debt	(9)us-gaap_RepaymentsOfLongTermDebt	(229)us-gaap_RepaymentsOfLongTermDebt	(270)us-gaap_RepaymentsOfLongTermDebt
Dividends paid	(230)us-gaap_PaymentsOfDividendsCommonStock	(178)us-gaap_PaymentsOfDividendsCommonStock	(184)us-gaap_PaymentsOfDividendsCommonStock
Net cash flows from financing activities	(239)	(407)	(322)
Net change in cash and cash equivalents	94	(75)	135
Cash and cash equivalents at beginning of period	126	201	66
Cash and cash equivalents at end of period	$ 220	$ 126	$ 201

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