Borrowings and Other Financing Instruments, Long-Term Borrowings (Details) (First Mortgage Bonds, Series Due March 15, 2044, USD $)	1 Months Ended
	Mar. 31, 2014
First Mortgage Bonds | Series Due March 15, 2044
Debt Instrument [Line Items]
Face amount	$ 300,000,000
Interest rate, stated percentage	4.30%
Maturity date	Mar. 15, 2044