Commitments and Contingencies, Legal Contingencies (Details) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended	13 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Pacific Northwest FERC Refund Proceeding [Member]	Sep. 30, 2014 PSCo Pacific Northwest FERC Refund Proceeding [Member] Factor	Jun. 30, 2001 PSCo Pacific Northwest FERC Refund Proceeding [Member]
Legal Contingencies [Abstract]
Accrual for legal contingency					$ 0	$ 0
Minimum amount of damages claimed by plaintiff						34,000,000
Sales to the City of Seattle	1,049,111,000	1,044,300,000	3,246,358,000	3,128,186,000			50,000,000
Estimated City of Seattle's claim for refunds not including interest						$ 28,000,000
Number of factors considered in assessment						2