Business Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Financial data by business segment
Operating revenues	$ 620,631	$ 648,847
Net income (loss) attributable to common shareholders	(8,257)	(15,135)
Assets	13,183,914		13,111,018
Regulated electricity segment
Financial data by business segment
Operating revenues	620,000	648,000
Net income (loss) attributable to common shareholders	(6,000)	(15,000)
Assets	13,142,000		13,068,000
All other
Financial data by business segment
Operating revenues	1,000	1,000
Net income (loss) attributable to common shareholders	(2,000)
Assets	$ 42,000		$ 43,000