Consolidated Income Statements (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating Revenues	$ 4,246.4	$ 4,486.4	$ 4,202.5
Operating Expenses
Fuel and purchased power	1,098.6	1,169.7	1,099.9
Cost of gas sold	545.8	728.7	751.5
Other operation and maintenance	1,116.1	1,256.8	1,327.5
Depreciation and amortization	364.2	330.2	305.6
Property and revenue taxes	121.4	113.7	106.0
Total Operating Expenses	3,246.1	3,599.1	3,590.5
Amortization of Gain	0	0	198.4
Operating Income	1,000.3	887.3	810.4
Income (Loss) from Equity Method Investments	65.5	61.6	59.9
Other Income and Deductions, net	34.8	62.7	40.2
Interest Expense, net	248.2	235.8	206.4
Income (Loss) from Continuing Operations Before Income Taxes	852.6	776.7	704.3
Income Tax Expense	306.3	263.9	249.9
Income from Continuing Operations	546.3	512.8	454.4
Income from Discontinued Operations, Net of Tax	0	13.4	2.1
Net Income	546.3	526.2	456.5
Earnings Per Share (Basic)
Continuing Operations	$ 2.37	$ 2.20	$ 1.94
Discontinued Operations	$ 0.00	$ 0.06	$ 0.01
Total Earnings Per Share (Basic)	$ 2.37	$ 2.26	$ 1.95
Earnings Per Share (Diluted)
Continuing Operations	$ 2.35	$ 2.18	$ 1.92
Discontinued Operations	$ 0.00	$ 0.06	$ 0.01
Total Earnings Per Share (Diluted)	$ 2.35	$ 2.24	$ 1.93
Weighted Average Common Shares Outstanding (Millions)
Basic	230.2	232.6	233.8
Diluted	232.8	235.4	236.7
Transmission Affiliate [Member]
Operating Expenses
Income (Loss) from Equity Method Investments	$ 65.7	$ 62.5	$ 60.1