Income Taxes: Effective Tax Rate Differences from Statutory Tax Rates (Details)		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Federal statutory rate		35.00%	35.00%	35.00%
Amortization of excess deferred and investment tax credits		(0.10%)	(0.30%)	(0.30%)
Equity AFUDC		(0.60%)	(0.10%)	0.00%
Flow through adjustments	[1]	(0.90%)	(1.90%)	(2.50%)
Tax credits		(0.00%)	(0.20%)	(0.80%)
Other		0.00%	0.50%	(0.60%)
Effective Income Tax Rate		33.40%	33.00%	30.80%

[1] The flow-through adjustments relate primarily to an accounting method change for tax purposes that allows us to take a current tax deduction for repair costs that continue to be capitalized for book purposes. We recorded a deferred income tax liability in recognition of the temporary difference created between book and tax treatment and we flowed the tax benefit through to our customers in the form of lower rates as a result of a rate case settlement that occurred during 2010. A regulatory asset was established to reflect the recovery of future increases in taxes payable from customers as the temporary differences reverse. As a result of this regulatory treatment, we continue to record a tax benefit consistent with the flow through method.