COMMON EQUITY - EARNINGS PER SHARE (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator:
Net income from continuing operations	$ 82.9	$ 39.4	$ 244.2	$ 217.7
Discontinued operations, net of tax	1.1	(0.6)	0.9	4.7
Preferred stock dividends of subsidiary	(0.7)	(0.7)	(2.3)	(2.3)
Noncontrolling interest in subsidiaries	0	0	0.1	0.1
Net income attributed to common shareholders	83.3	38.1	242.9	220.2
Net income attributed to common shareholders — diluted	82.5	38.0	242.9	220.1
Denominator:
Average shares of common stock — basic	80.2	79.8	80.2	79.3
Average shares of common stock - diluted	81.1	80.2	80.6	79.9
Earnings per common share
Basic (in dollars per share)	$ 1.04	$ 0.48	$ 3.03	$ 2.78
Diluted (in dollars per share)	$ 1.02	$ 0.47	$ 3.01	$ 2.76
Stock-based compensation
Numerator:
Effect of dilutive securities	0	(0.1)	0	(0.1)
Denominator:
Effect of dilutive securities	0.6	0.4	0.4	0.4
Deferred compensation
Numerator:
Effect of dilutive securities	$ (0.8)	$ 0	$ 0	$ 0
Denominator:
Effect of dilutive securities	0.3	0	0	0.2