CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
OPERATING REVENUES
Regulated electricity	$ 3,237,194	$ 3,180,678	$ 3,149,187
Other revenues	4,185	8,521	4,469
Total	3,241,379	3,189,199	3,153,656
OPERATING EXPENSES
Regulated electricity fuel and purchased power	1,009,464	1,046,815	1,178,620
Operations and maintenance	904,286	870,185	822,300
Depreciation and amortization	427,054	414,479	407,354
Taxes other than income taxes	147,408	135,328	123,270
Other expenses	6,659	7,509	5,984
Total	2,494,871	2,474,316	2,537,528
OPERATING INCOME	746,508	714,883	616,128
OTHER INCOME (DEDUCTIONS)
Allowance for equity funds used during construction (Note 1)	23,707	22,066	14,999
Other income (Note 19)	3,111	6,387	5,159
Other expense (Note 19)	(10,451)	(9,921)	(14,300)
Total	16,367	18,532	5,858
INTEREST EXPENSE
Interest charges	241,995	244,174	237,766
Allowance for borrowed funds used during construction (Note 1)	(18,358)	(16,479)	(10,379)
Total	223,637	227,695	227,387
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	539,238	505,720	394,599
INCOME TAXES (Note 4)	183,604	160,869	138,551
INCOME FROM CONTINUING OPERATIONS	355,634	344,851	256,048
INCOME (LOSS) FROM DISCONTINUED OPERATIONS
Net of income tax expense (benefit) of $7,418, $16,260 and $(109,641) (Note 21)	11,306	25,358	(183,284)
NET INCOME	366,940	370,209	72,764
Less: Net income attributable to noncontrolling interests (Note 20)	27,467	20,156	4,434
Net income attributable to common shareholders	339,473	350,053	68,330
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING - BASIC (in shares)	109,053	106,573	101,161
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING - DILUTED (in shares)	109,864	107,138	101,264
EARNINGS PER WEIGHTED - AVERAGE COMMON SHARE OUTSTANDING
Income from continuing operations attributable to common shareholders - basic (in dollars per share)	$ 3.01	$ 3.05	$ 2.34
Net income attributable to common shareholders - basic (in dollars per share)	$ 3.11	$ 3.28	$ 0.68
Income from continuing operations attributable to common shareholders - diluted (in dollars per share)	$ 2.99	$ 3.03	$ 2.34
Net income attributable to common shareholders - diluted (in dollars per share)	$ 3.09	$ 3.27	$ 0.67
DIVIDENDS DECLARED PER SHARE (in dollars per share)	$ 2.10	$ 2.10	$ 2.10
AMOUNTS ATTRIBUTABLE TO COMMON SHAREHOLDERS:
Income from continuing operations, net of tax	328,110	324,688	236,839
Discontinued operations, net of tax	11,363	25,365	(168,509)
Net income attributable to common shareholders	$ 339,473	$ 350,053	$ 68,330