CONSOLIDATED BALANCE SHEETS (UNAUDITED) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Current assets
Cash and cash equivalents	$ 112,960	$ 82,323
Accounts receivable, net	789,209	718,046
Accrued unbilled revenues	586,761	663,363
Inventories	447,709	535,574
Regulatory assets	369,206	352,977
Derivative instruments	59,554	69,013
Deferred income taxes	93,193	32,528
Prepayments and other	246,079	171,315
Total current assets	2,704,671	2,625,139
Property, plant and equipment, net	24,219,231	23,809,348
Other assets
Nuclear decommissioning fund and other investments	1,663,648	1,617,865
Regulatory assets	2,711,881	2,762,029
Derivative instruments	111,168	126,297
Other	177,076	200,008
Total other assets	4,663,773	4,706,199
Total assets	31,587,675	31,140,686
Current liabilities
Current portion of long-term debt	6,929	258,155
Short-term debt	425,000	602,000
Accounts payable	932,547	959,093
Regulatory liabilities	193,658	168,858
Taxes accrued	415,081	334,441
Accrued interest	135,532	162,494
Dividends payable	133,238	131,748
Derivative instruments	30,762	32,482
Other	253,770	287,802
Total current liabilities	2,526,517	2,937,073
Deferred credits and other liabilities
Deferred income taxes	4,643,378	4,434,909
Deferred investment tax credits	81,674	82,761
Regulatory liabilities	1,077,606	1,059,939
Asset retirement obligations	1,741,707	1,719,796
Derivative instruments	230,272	242,866
Customer advances	259,200	252,888
Pension and employee benefit obligations	979,520	1,163,265
Other	250,679	229,207
Total deferred credits and other liabilities	9,264,036	9,185,631
Commitments and contingencies
Capitalization
Long-term debt	10,642,009	10,143,905
Common stock - 1,000,000,000 shares authorized of $2.50 par value; 494,755,061 and 487,959,516 shares outstanding at March 31, 2013 and Dec. 31, 2012, respectively	1,236,888	1,219,899
Additional paid in capital	5,515,513	5,353,015
Retained earnings	2,516,332	2,413,816
Accumulated other comprehensive loss	(113,620)	(112,653)
Total common stockholders' equity	9,155,113	8,874,077
Total liabilities and equity	$ 31,587,675	$ 31,140,686