CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) (USD $) In Millions, unless otherwise specified	Total	Common Stock	Premium on Common Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest	Treasury Stock
Balance at Dec. 31, 2012	$ 3,072.4	$ 1.0	$ 1,046.4	$ 1,772.4	$ (49.1)	$ 305.2	$ (3.5)
Changes in Stockholders' Equity
Net income	28.0	0	0	23.1	0	4.9	0
Other comprehensive income, net of tax	0.9	0	0	0	0.8	0.1	0
Dividends declared on common stock	(41.4)	0	0	(41.4)	0	0	0
Issuance of common stock	3.2	0	3.2	0	0	0	0
Stock-based compensation and other	(8.3)	0	(10.9)	0	0	(0.9)	3.5
Distributions to noncontrolling interest partners	(2.5)	0	0	0	0	(2.5)	0
Balance at Mar. 31, 2013	3,052.3	1.0	1,038.7	1,754.1	(48.3)	306.8	0
Balance at Dec. 31, 2013	3,037.1	2.0	1,071.6	1,991.7	(28.2)	0	0
Changes in Stockholders' Equity
Net income	49.3	0	0	49.3	0	0	0
Other comprehensive income, net of tax	0.3	0	0	0	0.3	0	0
Dividends declared on common stock	(44.9)	0	0	(44.9)	0	0	0
Issuance of common stock	3.4	0	3.4	0	0	0	0
Stock-based compensation and other	(7.4)	0	(7.4)	0	0	0	0
Distributions to noncontrolling interest partners	0
Balance at Mar. 31, 2014	$ 3,037.8	$ 2.0	$ 1,067.6	$ 1,996.1	$ (27.9)	$ 0	$ 0