Share Capital (Narrative) (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Shares repurchased	1.2	7.4	13.9
Cost of repurchased shares	$ 50,000,000	$ 269,600,000	$ 470,500,000
Shares withheld to meet employees' tax withholding obligations		2.1	2.4
Fair values of shares withheld		73,300,000	64,900,000
Stock repurchase program, authorized amount			1,500,000,000
Share repurchase plan, remaining authorized amount	1,226,800,000	1,226,800,000	1,496,500,000
Treasury stock shares	69.4	69.4	66.8
Treasury shares held, as unvested restricted stock awards	8.9	8.9	9.5
Common shares market price (per share)		$ 39.52
Treasury shares market value		$ 2,700,000,000