Debt (Credit Facilities) (Details) (USD $)	0 Months Ended	1 Months Ended	6 Months Ended	12 Months Ended
	Aug. 01, 2011	Oct. 31, 2010	Jun. 30, 2011	Dec. 31, 2010	Aug. 31, 2011
Line of credit facility, maximum borrowing capacity			$ 1,500,000,000		$ 1,500,000,000
Line of credit facility, expiration date	August 1, 2016
Parent company borrowing limit under credit facility			875,000,000
Subsidiary borrowing limit under parents credit facility			500,000,000
Combined maximum amount of credit facility available to utility subsidiaries			625,000,000
Unsecured credit agreements		200,000,000
Borrowing capacity under the credit facilities			1,400,000,000	1,200,000,000
Combined cash and borrowings capacity			$ 595,000,000	$ 462,000,000
Bi-lateral unsecured credit agreements		364
Before Amendment [Member]
Line of credit facility, expiration date	May 2, 2012
PHI [Member]
Line of credit facility, expiration date			October 26, 2011