Share Capital - Narrative (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	2 Months Ended	12 Months Ended	3 Months Ended	9 Months Ended
	Feb. 22, 2013 2012 Repurchase Authorization	Dec. 31, 2012 2012 Repurchase Authorization	Sep. 30, 2013 2013 Repurchase Authorization	Sep. 30, 2013 2013 Repurchase Authorization	Sep. 30, 2013 Stock options	Sep. 30, 2013 Restricted stock awards	Sep. 30, 2013 Restricted stock units	Sep. 30, 2013 Performance units	Sep. 30, 2013 Minimum [Member]	Sep. 30, 2013 Minimum [Member] Performance units	Sep. 30, 2013 Maximum [Member]	Sep. 30, 2013 Maximum [Member] Performance units
Shareholders Equity Disclosure [Line Items]
Stock Repurchase Program, Authorized Amount		$ 750,000,000		$ 850,000,000
Stock Repurchased and Retired During Period, Shares	3.8	18.3	4.8	17.7
Stock Repurchased and Retired During Period, Value	98,300,000	401,600,000	150,000,000	523,300,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	250,000,000			425,000,000
Stock Repurchase Program, Stock repurchased during period average price per share			$ 31.03	$ 29.59
Weighted Average Grant Date Fair Value Per Stock Option					$ 8.34
Number of Stock Options Granted During the Period					1.0
Number of Awards Granted During the Period						0.2	1.8	0.7
Aggregate Grant Date Fair Value of Award						$ 5,300,000	$ 51,500,000	$ 17,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period							3 years	3 years	3 years		4 years
Share Based Compensation Arrangement Performance Units Maximum Share Payout Number								1.4
Performance Units Final Payout Percentage Of Grant Amount										0.00%		200.00%