Share Capital (Details) - Authorized and issued (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012
Equity Class Of Treasury Stock [Line Items]
Treasury Stock Value Retired Par Value Method		$ 350.0
Treasury Stock, Shares, Retired (in Shares)		16.2
Common Class A [Member] | 2010 Repurchase Authorization [Member]
Equity Class Of Treasury Stock [Line Items]
Stock Repurchase Program Authorized Amount		190.0
Common Class A [Member] | 2012 Repurchase Authorization [Member]
Equity Class Of Treasury Stock [Line Items]
Stock Repurchase Program Authorized Amount		750.0
Stock Repurchase Program Remaining Authorized Repurchase Amount		400.0
Treasury Stock Value Retired Par Value Method	$ 125.0
Treasury Stock, Shares, Retired (in Shares)	5.3