Earnings Per Share Data (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Mar. 31, 2011	Jun. 30, 2012	Jun. 30, 2011
Schedule of Earnings Per Share [Line Items]
Shares issued from the conversion of convertible securities			6,999,887
Earnings Per Share Reconciliation [Abstract]
Net income available to common stockholders for purposes of computing basic earnings per share	$ 120.4	$ 70.7		$ 195.3	$ 133.3
Effect of dividends on conversion of convertible preferred stock	0	0		0	1.4
Net income available to common stockholders for purposes of computing diluted earnings per share	$ 120.4	$ 70.7		$ 195.3	$ 134.7
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Basic shares	109,689,000	109,428,000		109,657,000	106,858,000
Effect of dilution	367,000	382,000		371,000	2,918,000
Diluted shares	110,056,000	109,810,000		110,028,000	109,776,000
Earnings Per Share [Abstract]
Basic earnings per share	$ 1.10	$ 0.65		$ 1.78	$ 1.25
Diluted earnings per share	$ 1.09	$ 0.64		$ 1.77	$ 1.23
Stock Options [Member]
Potentially Dilutive Shares Excluded from the Calculation [Abstract]
Stock options excluded as their inclusion would be anti-dilutive	69,000	97,000		69,000	101,000