Employee Share-Based Incentive Compensation Plans (WTM Restricted Shares) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2013 Restricted Share Cliff Vesting in January 2016 [Member]	Dec. 31, 2012 Restricted Share Cliff Vesting in January 2015 [Member]	Dec. 31, 2012 Restricted Share Vesting Beginning in February 2014 [Member] Installment	Dec. 31, 2012 Restricted Share Cliff Vesting in July 2015 [Member]	Dec. 31, 2011 Restricted Share Cliff Vesting in January 2014 [Member]	Dec. 31, 2011 W T M Incentive Plan		Dec. 31, 2013 W T M Incentive Plan Restricted Stock		Dec. 31, 2012 W T M Incentive Plan Restricted Stock		Dec. 31, 2012 Restricted Share Vested in December 2012 [Member] Restricted Stock
Target Performance Share activity
Beginning of period (in shares)							46,250		69,910		72,000
Issued (in shares)		25,720	27,960	3,000	1,200	27,250	27,250		25,720		32,160
Vested (in shares)							(1,500)	[1]	(1,500)	[1]	(32,945)	[1]
Assumed forfeitures and cancellations (in shares)	0						0		0		(1,305)
Ending of period (in shares)							72,000		94,130		69,910
Unamortized grant date fair value
Beginning balance							$ 14.1		$ 16.8		$ 13.3
Issued							9.9		14.4		15.7
Assumed forfeitures and cancellations							0		0		(0.2)
Expense recognized							(10.7)		(14.2)		(12.0)
Ending balance							$ 13.3		$ 17.0		$ 16.8
Number of restricted shares installments				2									5,000

[1] During 2012, the Compensation Committee accelerated the vesting date for an installment of 5,000 restricted shares from January 20, 2013 to December 31, 2012.