Employee Stock and Incentive Plans - Non-Qualified Stock Options (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2008
Number of Options [Abstract]
Outstanding as of January 1,	108,299		395,678		460,234
Granted	0	[1]	0	[1]	0	[1]
Exercised	(42,020)		(287,379)		(49,075)
Forfeited	0		0		(15,481)
Outstanding as of December 31,	66,279		108,299		395,678
Exercisable as of December 31,	66,279		108,299		395,678
Weighted Average Exercise Price [Abstract]
Outstanding as of January 1,	$ 44.10		$ 42.28		$ 41.68
Granted	$ 0.00	[1]	$ 0.00	[1]	$ 0.00	[1]
Exercised	$ 43.65		$ 41.60		$ 35.84
Forfeited	$ 0.00		$ 0.00		$ 44.86
Outstanding as of December 31,	$ 44.39		$ 44.10		$ 42.28
Exercisable as of December 31,	$ 44.39		$ 43.17		$ 41.71
Weighted Average Grant-Date Intrinsic Value of Options Granted							$ 6.18
Proceeds from Stock Options Exercised	$ 1.8
Total Intrinsic Value of Options Exercised	$ 0.4		$ 2.2		$ 0.3

[1] Stock options have not been granted since 2008. The weighted-average grant-date intrinsic value of options granted in 2008 was $6.18.