Condensed Statements of Shareholders' Equity (USD $) In Millions, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]
Balance at Dec. 31, 2011	$ 985.8	$ 80.1	$ 852.0	$ (294.2)	$ 347.9
Balance (in shares) at Dec. 31, 2011		80.1
Net income	86.3	0	0	0	86.3
Other comprehensive income (loss)	8.3	0	0	8.3	0
Dividends paid:
Common stock ($0.40 per share)	(32.0)	0	0	0	(32.0)
Common stock repurchased and retired	(3.1)	(0.2)	(2.9)	0	0
Common stock repurchased and retired (in shares)	(0.2)	(0.2)
Common stock issued for:
Stock options exercised	0.5	0	0.5	0	0
Stock options exercised (in shares)	0	0
Other transactions	1.0	0.1	0.9	0	0
Other transactions (in shares)		0.1
Stock-based compensation	0.9	0	0.9	0	0
Balance at Jun. 30, 2012	1,047.7	80.0	851.4	(285.9)	402.2
Balance (in shares) at Jun. 30, 2012		80.0
Balance at Dec. 31, 2012	998.4	80.2	856.1	(371.3)	433.4
Balance (in shares) at Dec. 31, 2012		80.2
Net income	84.2	0	0	0	84.2
Other comprehensive income (loss)	(1.2)	0	0	(1.2)	0
Dividends paid:
Common stock ($0.40 per share)	(32.1)	0	0	0	(32.1)
Common stock repurchased and retired	(14.7)	(0.6)	(14.1)	0	0
Common stock repurchased and retired (in shares)	(0.6)	(0.6)
Common stock issued for:
Stock options exercised	6.8	0.3	6.5	0	0
Stock options exercised (in shares)	0.3	0.3
Other transactions	1.4	0.1	1.3	0	0
Other transactions (in shares)		0.1
Stock-based compensation	2.2	0	2.2	0	0
Balance at Jun. 30, 2013	$ 1,045.0	$ 80.0	$ 852.0	$ (372.5)	$ 485.5
Balance (in shares) at Jun. 30, 2013		80.0