STATEMENTS OF INCOME (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
OPERATING REVENUES	$ 2,211.5	$ 2,109.9	$ 1,751.2
COST OF GOODS SOLD (exclusive of depreciation and amortization shown below)	1,013.5	1,000.2	796.3
Gross margin on revenues	1,198.0	1,109.7	954.9
OPERATING EXPENSES
Other operation and maintenance	436.0	418.1	348.0
Depreciation and amortization	216.1	208.7	187.4
Impairment of assets	0	0	0.3
Taxes other than income	73.6	69.2	65.1
Total operating expenses	725.7	696.0	600.8
OPERATING INCOME	472.3	413.7	354.1
OTHER INCOME (EXPENSE)
Interest income	0.5	0.1	1.1
Allowance for equity funds used during construction	20.4	11.4	15.1
Other income	8.0	6.5	20.4
Other expense	(8.4)	(1.6)	(6.7)
Net other income	20.5	16.4	29.9
INTEREST EXPENSE
Interest on long-term debt	118.7	104.7	96.5
Allowance for borrowed funds used during construction	(10.4)	(5.5)	(8.3)
Interest on short-term debt and other interest charges	3.3	4.2	5.4
Interest expense	111.6	103.4	93.6
INCOME BEFORE TAXES	381.2	326.7	290.4
INCOME TAX EXPENSE	117.9	111.0	90.0
NET INCOME	$ 263.3	$ 215.7	$ 200.4