Borrowings and Other Financing Instruments, Credit Facility (Details) (USD $)	Jun. 30, 2014		Dec. 31, 2013
Credit Facility [Abstract]
Credit facility	$ 700,000,000	[1]
Drawn	263,300,000	[2]
Available	436,700,000
Credit facility bank borrowings outstanding	$ 0		$ 0

[1] Credit facility expires in July 2017.

[2] Includes outstanding commercial paper and letters of credit.