CONDENSED CONSOLIDATED STATEMENTS OF INCOME (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Income Statement [Abstract]
Utility revenues	$ 1,616.7	$ 1,123.8
Nonregulated revenues	1,308.2	554.4
Total revenues	2,924.9	1,678.2
Utility cost of fuel, natural gas, and purchased power	960.2	565.1
Nonregulated cost of sales	1,247.5	436.8
Operating and maintenance expense	364.6	295.1
Depreciation and amortization expense	71.3	60.9
Taxes other than income taxes	28.1	27.2
Operating income	253.2	293.1
Earnings from equity method investments	22.9	22.3
Miscellaneous income	6.0	5.7
Interest expense	39.1	29.3
Other expense	(10.2)	(1.3)
Income before taxes	243.0	291.8
Provision for income taxes	89.8	109.6
Net income from continuing operations	153.2	182.2
Discontinued operations, net of tax	(0.1)	6.1
Net income	153.1	188.3
Preferred stock dividends of subsidiary	(0.8)	(0.8)
Noncontrolling interest in subsidiaries	0.1	0
Net income attributed to common shareholders	$ 152.4	$ 187.5
Average shares of common stock
Basic (in shares)	80.2	78.7
Diluted (in shares)	80.5	79.3
Earnings per common share (basic)
Net income from continuing operations (in dollars per share)	$ 1.90	$ 2.30
Discontinued operations, net of tax (in dollars per share)	$ 0.00	$ 0.08
Earnings per common share (basic) (in dollars per share)	$ 1.90	$ 2.38
Earnings per common share (diluted)
Net income from continuing operations (in dollars per share)	$ 1.89	$ 2.29
Discontinued operations, net of tax (in dollars per share)	$ 0.00	$ 0.08
Earnings per common share (diluted) (in dollars per share)	$ 1.89	$ 2.37
Dividends per common share declared (in dollars per share)	$ 0.68	$ 0.68