Basis of Presentation (Details) $ in Millions	12 Months Ended
	Dec. 31, 2014 USD ($)	Dec. 31, 2016 mi² shares retail_customers
Basis of Presentation [Abstract]
Proceeds from Legal Settlements | $	$ 6
Incorporated Cities		51
Service Area Sq Miles | mi²		4,000
Number of Retail Customers | retail_customers		863,000
Service area population		1,900,000
Percent of State's Population		46.00%
Entity Number of Employees		2,752
Number of Union Employees		783
Number of Union Employees Subject to Agreement A		730
Number of Union Employees Subject to Agreement B		53
Proceeds from Insurance Settlement, Investing Activities | $	3
Proceeds from Sale of Productive Assets | $	$ 5