CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Millions	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	150.1	0.0	0.0	150.1	0.0
Other comprehensive income, net of tax	0.6	0.0	0.0	0.0	0.6
Dividends declared on common stock	(89.7)	0.0	0.0	(89.7)	0.0
Issuance of common stock	6.7	0.0	6.7	0.0	0.0
Stock-based compensation	(5.0)	0.0	(5.0)	0.0	0.0
Balance at Jun. 30, 2014	3,099.8	2.0	1,073.3	2,052.1	(27.6)
Balance at Dec. 31, 2014	3,244.4	2.0	1,085.6	2,198.2	(41.4)
Changes in Stockholders' Equity
Net income	130.7	0.0	0.0	130.7	0.0
Other comprehensive income, net of tax	0.9	0.0	0.0	0.0	0.9
Dividends declared on common stock	(99.8)	0.0	0.0	(99.8)	0.0
Issuance of common stock	6.8	0.0	6.8	0.0	0.0
Stock-based compensation	3.0	0.0	3.0	0.0	0.0
Balance at Jun. 30, 2015	$ 3,286.0	$ 2.0	$ 1,095.4	$ 2,229.1	$ (40.5)