Compensation and Benefit Plans (Performance Shares Valuation Assumptions) (Details)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Performance Benefits Classified As Equity Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate	0.40%		1.20%		1.30%
Expected volatility	13.20%		20.40%		21.60%
Performance Shares Classified As Liability Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	12.10%	[1]	15.90%	[1]	20.60%	[1]
Performance Benefits Classified As Liability Awards 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate	0.40%	[1]
Performance Benefits Classified As Liability Awards 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate	0.20%	[1]	0.30%	[1]
Performance Benefits Classified As Liability Awards 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate			0.20%	[1]	0.60%	[1]

[1] The portion of performance shares classified as share-based liability awards are revalued at each reporting period.