Borrowings and Other Financing Instruments Borrowings and Other Financing Instruments, Long-Term Borrowings and Other Financing Instruments (Details) (First Mortgage Bonds, USD $)	1 Months Ended
	Jun. 30, 2014
Series No. 3 Due June 15, 2024
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 150,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.30%
Debt Instrument, Maturity Date	Jun. 15, 2024
Issued Collateral on Series G Senior Note Due Dec. 1, 2018
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 250,000,000
Debt Instrument, Interest Rate, Stated Percentage	8.75%
Debt Instrument, Maturity Date	Dec. 01, 2018
Previously Issued Series G Senior Note Due Dec. 1, 2018
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	8.75%
Debt Instrument, Maturity Date	Dec. 01, 2018