Employee Share-Based Incentive Compensation Plans (WTM Non-Qualified and Qualified Options) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended	1 Months Ended				1 Months Ended	12 Months Ended
	Dec. 31, 2010	May 31, 2010 Non-Qualified Options	May 31, 2010 Before Amendments Non-Qualified Options	Jan. 31, 2007 Before Amendments Non-Qualified Options	May 26, 2010 Before Amendments Non-Qualified Options	May 31, 2010 Grant Amendments Non-Qualified Options	Dec. 31, 2011 Grant Amendments Non-Qualified Options	Dec. 31, 2010 Grant Amendments Non-Qualified Options	May 26, 2010 Grant Amendments Non-Qualified Options
Share-based compensation arrangement by share-based payment award
Granted (in shares)				200,000
Expiration date				7 years
Vesting period (in years)				5 years
Initial exercise price (in dollars per share)				$ 650
Annual percentage increase in exercise price				5.00%
Options, fair value				$ 27.2	$ 3.5				$ 4.4
Extension of contractual term (in years)						3 years
Exercise price (in dollar per share)									$ 742
Number of shares extinguished									75,000
Threshold for in-the-money potential						100
Limit on value of in-the-money options over $100 million (as a percent)						50.00%
Unamortized grant date fair value					9.0
Expected dividend yield (as a percent)			0.32%	1.40%		0.32%
Expected volatility (as a percent)			41.00%	29.70%		34.00%
Risk-free rate (as a percent)			1.57%	1.10%		2.43%
Fair value assumptions risk free Interest rate less escalator				4.70%
Forfeiture (as a percent)			0.00%	0.00%		0.00%
Expected life (in years)			3 years 8 months 1 day	7 years		6 years 8 months 1 day
Share-based compensation expense, amortized before modification Date									18.2
Restricted shares issued to key managment personnel (in shares)	(2,400)
Expense recognized		$ 8.7					$ 0.1	$ 11.9