CONSOLIDATED STATEMENTS OF EQUITY (USD $) In Millions, unless otherwise specified	Total	Total Common Shareholders' Equity	Shares in Deferred Compensation Trust	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Preferred Stock of Subsidiary	Noncontrolling Interest in Subsidiaries
Balance at Dec. 31, 2010	$ 2,957.0	$ 2,905.8	$ (18.5)	$ 77.8	$ 2,540.4	$ 350.8	$ (44.7)	$ 51.1	$ 0.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributed to common shareholders	227.4	227.4	0	0	0	227.4	0	0	0
Other comprehensive income	2.2	2.2	0	0	0	0	2.2	0	0
Issuance of common stock	22.2	22.2	0	0.5	21.7	0	0	0	0
Stock-based compensation	5.4	5.4	0	0	7.5	(2.1)	0	0	0
Dividends on common stock (dividends per common share of $2.72)	(211.8)	(211.8)	0	0	0	(211.8)	0	0	0
Shares issued to and purchased for the deferred compensation trust	(1.0)	(1.0)	(3.3)		2.3
Other	11.2	11.2	4.7	0	7.2	(0.7)	0	0	0
Balance at Dec. 31, 2011	3,012.6	2,961.4	(17.1)	78.3	2,579.1	363.6	(42.5)	51.1	0.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributed to common shareholders	281.2	281.4	0	0	0	281.4	0	0	(0.2)
Other comprehensive income	1.6	1.6	0	0	0	0	1.6	0	0
Issuance of common stock	0	0	0	0	0	0	0	0	0
Stock-based compensation	(4.8)	(4.8)	0	0	(4.1)	(0.7)	0	0	0
Dividends on common stock (dividends per common share of $2.72)	(211.9)	(211.9)	0	0	0	(211.9)	0	0	0
Shares issued to and purchased for the deferred compensation trust	(3.2)	(3.2)	(3.2)
Other	1.3	1.3	2.6	0	(0.4)	(0.9)	0	0	0
Balance at Dec. 31, 2012	3,076.8	3,025.8	(17.7)	78.3	2,574.6	431.5	(40.9)	51.1	(0.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributed to common shareholders	351.7	351.8	0	0	0	351.8	0	0	(0.1)
Other comprehensive income	17.7	17.7	0	0	0	0	17.7	0	0
Issuance of common stock	79.8	79.8	0	1.5	78.3	0	0	0	0
Stock-based compensation	0.3	0.3	0	0	1.0	(0.7)	0	0	0
Dividends on common stock (dividends per common share of $2.72)	(214.6)	(214.6)	0	0	0	(214.6)	0	0	0
Net contributions from noncontrolling parties	1.0	0	0	0	0	0	0	0	1.0
Shares issued to and purchased for the deferred compensation trust	0	0	(6.3)	0.1	6.2	0	0	0	0
Other	0.7	0.5	1.0	0	0.4	(0.9)	0	0	0.2
Balance at Dec. 31, 2013	$ 3,313.4	$ 3,261.3	$ (23.0)	$ 79.9	$ 2,660.5	$ 567.1	$ (23.2)	$ 51.1	$ 1.0