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	3 Months Ended
	Jun. 30, 2014 Series No. 3 Due June 15, 2024	Jun. 30, 2014 Issued Collateral on Series G Senior Note Due Dec. 1, 2018 [Member]	Jun. 30, 2014 Previously Issued Series G Senior Note Due Dec. 1, 2018 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 150,000,000	$ 250,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.30%	8.75%	8.75%
Debt Instrument, Maturity Date	Jun. 15, 2024	Dec. 01, 2018	Dec. 01, 2018