Consolidated Condensed Income Statements (Unaudited) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Operating Revenues	$ 1,012.3	$ 944.7	$ 2,287.5	$ 2,135.9
Operating Expenses
Fuel and purchased power	276.1	258.7	547.1	512.5
Cost of gas sold	115.2	75.0	385.3	312.5
Other operation and maintenance	265.4	267.9	553.5	554.2
Depreciation and amortization	96.7	90.3	192.2	177.9
Property and revenue taxes	29.4	30.2	58.9	60.5
Total Operating Expenses	782.8	722.1	1,737.0	1,617.6
Operating Income	229.5	222.6	550.5	518.3
Income (Loss) from Equity Method Investments	17.2	16.1	33.9	31.7
Other Income, net	5.8	8.6	10.2	24.6
Interest Expense, net	63.3	61.5	128.3	120.4
Income from Continuing Operations Before Income Taxes	189.3	185.9	466.3	454.3
Income Tax Expense	70.3	66.6	170.7	162.9
Net Income	119.0	119.3	295.6	291.4
Earnings Per Share (Basic)
Continuing operations	$ 0.52	$ 0.52	$ 1.29	$ 1.26
Earnings Per Share (Diluted)
Continuing operations	$ 0.52	$ 0.51	$ 1.28	$ 1.25
Weighted Average Common Shares Outstanding (Millions)
Basic	228.4	230.4	228.6	230.5
Diluted	230.5	233.1	230.8	233.1
Dividends Per Share of Common Stock	$ 0.34	$ 0.30	$ 0.68	$ 0.60
Transmission Affiliate [Member]
Operating Expenses
Income (Loss) from Equity Method Investments	$ 17.3	$ 16.2	$ 33.9	$ 31.8