CONSOLIDATED BALANCE SHEETS (UNAUDITED) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current assets
Cash and cash equivalents	$ 58,821	$ 82,323
Accounts receivable, net	719,069	718,046
Accrued unbilled revenues	626,294	663,363
Inventories	494,890	535,574
Regulatory assets	396,308	352,977
Derivative instruments	100,215	69,013
Deferred income taxes	158,350	32,528
Prepayments and other	264,253	171,315
Total current assets	2,818,200	2,625,139
Property, plant and equipment, net	24,813,411	23,809,348
Other assets
Nuclear decommissioning fund and other investments	1,622,978	1,617,865
Regulatory assets	2,727,210	2,762,029
Derivative instruments	100,313	126,297
Other	184,150	200,008
Total other assets	4,634,651	4,706,199
Total assets	32,266,262	31,140,686
Current liabilities
Current portion of long-term debt	282,042	258,155
Short-term debt	354,000	602,000
Accounts payable	998,607	959,093
Regulatory liabilities	205,112	168,858
Taxes accrued	242,339	334,441
Accrued interest	156,751	162,494
Dividends payable	139,240	131,748
Derivative instruments	29,897	32,482
Other	288,822	287,802
Total current liabilities	2,696,810	2,937,073
Deferred credits and other liabilities
Deferred income taxes	4,820,650	4,434,909
Deferred investment tax credits	80,587	82,761
Regulatory liabilities	1,070,059	1,059,939
Asset retirement obligations	1,762,959	1,719,796
Derivative instruments	222,575	242,866
Customer advances	261,684	252,888
Pension and employee benefit obligations	988,773	1,163,265
Other	245,443	229,207
Total deferred credits and other liabilities	9,452,730	9,185,631
Commitments and contingencies
Capitalization
Long-term debt	10,816,477	10,143,905
Common stock — 1,000,000,000 shares authorized of $2.50 par value; 497,295,719 and 487,959,516 shares outstanding at June 30, 2013 and Dec. 31, 2012, respectively	1,243,239	1,219,899
Additional paid in capital	5,595,906	5,353,015
Retained earnings	2,572,935	2,413,816
Accumulated other comprehensive loss	(111,835)	(112,653)
Total common stockholders’ equity	9,300,245	8,874,077
Total liabilities and equity	$ 32,266,262	$ 31,140,686