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)
Balance at Dec. 31, 2013	$ 3,037.1	$ 2.0	$ 1,071.6	$ 1,991.7	$ (28.2)
Changes in Stockholders' Equity
Net income	49.3	0	0	49.3	0
Other comprehensive income, net of tax	0.3	0	0	0	0.3
Dividends declared on common stock	(44.9)	0	0	(44.9)	0
Issuance of common stock	3.4	0	3.4	0	0
Stock-based compensation	(7.4)	0	(7.4)	0	0
Balance at Mar. 31, 2014	3,037.8	2.0	1,067.6	1,996.1	(27.9)
Balance at Dec. 31, 2014	3,244.4	2.0	1,085.6	2,198.2	(41.4)
Changes in Stockholders' Equity
Net income	43.2	0	0	43.2	0
Other comprehensive income, net of tax	0.2	0	0	0	0.2
Dividends declared on common stock	(49.9)	0	0	(49.9)	0
Issuance of common stock	3.2	0	3.2	0	0
Stock-based compensation	0.7	0	0.7	0	0
Balance at Mar. 31, 2015	$ 3,241.8	$ 2.0	$ 1,089.5	$ 2,191.5	$ (41.2)