STATEMENTS OF INCOME (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
OPERATING REVENUES	$ 2,141.2	$ 2,211.5	$ 2,109.9
COST OF GOODS SOLD (exclusive of depreciation and amortization shown below)	879.1	1,013.5	1,000.2
Gross margin on revenues	1,262.1	1,198.0	1,109.7
OPERATING EXPENSES
Other operation and maintenance	446.3	436.0	418.1
Depreciation and amortization	248.7	216.1	208.7
Taxes other than income	77.7	73.6	69.2
Total operating expenses	772.7	725.7	696.0
OPERATING INCOME	489.4	472.3	413.7
OTHER INCOME (EXPENSE)
Interest income	0.2	0.5	0.1
Allowance for equity funds used during construction	6.2	20.4	11.4
Other income	8.0	8.0	6.5
Other expense	(4.3)	(8.4)	(1.6)
Net other income	10.1	20.5	16.4
INTEREST EXPENSE
Interest on long-term debt	124.2	118.7	104.7
Allowance for borrowed funds used during construction	(3.5)	(10.4)	(5.5)
Interest on short-term debt and other interest charges	3.9	3.3	4.2
Interest expense	124.6	111.6	103.4
INCOME BEFORE TAXES	374.9	381.2	326.7
INCOME TAX EXPENSE	94.6	117.9	111.0
NET INCOME	$ 280.3	$ 263.3	$ 215.7