Employee Stock and Incentive Plans - Employee Stock Ownership Plan (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Employee Stock and Incentive Plans [Abstract]
ESOP Employer Loan, Description	In 1990, the ESOP issued a $75.0 million note (term not to exceed 25 years at 10.25 percent) to use as consideration for 2.8 million shares (1.9 million shares adjusted for stock splits) of our newly issued common stock. The note was refinanced in 2006 at 6 percent.
ESOP Compensation Expense	$ 7.4	$ 7.1	$ 6.5
Allocated	2.2	2.2	2.2
Unallocated	1.0	1.3	1.5
Total	3.2	3.5	3.7
Fair Value of Unallocated Shares	$ 42.0	$ 48.4	$ 49.0