Common Share Repurchases (details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Repurchase activity
Shares acquired to cover tax withholding costs and exercise costs		$ 73.0	$ 57.0
Board of Directors Approved Repurchase Authorization [Member]
Repurchase activity
Number of shares repurchased (in shares)	7,300,000	20,800,000
Cost of shares repurchased	$ 750.0	$ 2,150.0
Average cost per share	$ 102.81	$ 103.48
Remaining capacity under share repurchase authorization	$ 4,330.0	$ 4,330.0
Net shares acquired related to employee share-based compensation plans [Member]
Repurchase activity
Number of shares repurchased (in shares)	5,768	700,000
Shares acquired to cover tax withholding costs and exercise costs	$ 0.6	$ 73.0