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, 2010	$ 830.3	$ 79.6	$ 842.3	$ (261.8)	$ 170.2
Balance (in shares) at Dec. 31, 2010		79.6
Net income	175.8	0	0	0	175.8
Other comprehensive income	2.2	0	0	2.2	0
Dividends paid:
Common stock ($0.40 per share)	(32.0)	0	0	0	(32.0)
Common stock issued for:
Stock options exercised	9.3	0.5	8.8	0	0
Stock options exercised (in shares)	0.5	0.5
Other transactions	1.7	0.1	1.6	0	0
Other transactions (in shares)		0.1
Stock-based compensation	0.5	0	0.5	0	0
Balance at Jun. 30, 2011	987.8	80.2	853.2	(259.6)	314.0
Balance (in shares) at Jun. 30, 2011		80.2
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	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