CONDENSED STATEMENTS OF CHANGES IN STOCKHOLDER'S 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, 2011	$ 2,494.0	$ 100.9	$ 910.5	$ 1,485.1	$ (2.5)
Changes in Stockholders' Equity
Net income	12.1	0	0	12.1	0
Other comprehensive income (loss), net of tax	0
Stock-based compensation	0.6	0	0.6	0	0
Balance at Mar. 31, 2012	2,506.7	100.9	911.1	1,497.2	(2.5)
Balance at Dec. 31, 2012	2,703.1	100.9	913.1	1,690.4	(1.3)
Changes in Stockholders' Equity
Net income	13.0	0	0	13.0	0
Other comprehensive income (loss), net of tax	0.5	0	0	0	0.5
Dividends declared on common stock	(40.0)	0	0	(40.0)	0
Stock-based compensation	0.6	0	0.6	0	0
Balance at Mar. 31, 2013	$ 2,677.2	$ 100.9	$ 913.7	$ 1,663.4	$ (0.8)