Selected Balance Sheet Data (Tables)

3 Months Ended

Mar. 31, 2012

Selected Balance Sheet Data [Abstract]

Accounts receivable

(Thousands of Dollars)	March 31, 2012			Dec. 31, 2011
Accounts receivable, net
Accounts receivable	$	776,140		$	811,685
Less allowance for bad debts		(57,995	)		(58,565	)
	$	718,145		$	753,120

Inventories

Inventories
Materials and supplies	$	207,729	$	202,699
Fuel		176,874		236,023
Natural gas		89,756		179,510
	$	474,359	$	618,232

Property, plant and equipment

Property, plant and equipment, net
Electric plant	$	27,393,092		$	27,254,541
Natural gas plant		3,700,424			3,676,754
Common and other property		1,484,878			1,546,643
Plant to be retired (a)		115,401			151,184
Construction work in progress		1,315,390			1,085,245
Total property, plant and equipment		34,009,185			33,714,367
Less accumulated depreciation		(11,731,341	)		(11,658,351	)
Nuclear fuel		2,062,790			1,939,299
Less accumulated amortization		(1,667,948	)		(1,641,948	)
	$	22,672,686		$	22,353,367