Common Share Repurchases (details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2015	Jun. 30, 2014	Apr. 21, 2015
Repurchase activity
Shares acquired to cover tax withholding costs and exercise costs		$ 73.0	$ 56.0
Board of Directors Approved Repurchase Authorization [Member]
Repurchase activity
Number of shares repurchased (in shares)	7,900,000	13,500,000
Cost of shares repurchased	$ 800.0	$ 1,400.0
Average cost per share	$ 101.62	$ 103.85
Remaining capacity under share repurchase authorization	$ 5,080.0	$ 5,080.0
Additional share repurchase authorization				$ 5,000.0
Net shares acquired related to employee share-based compensation plans [Member]
Repurchase activity
Number of shares repurchased (in shares)	4,448	700,000
Shares acquired to cover tax withholding costs and exercise costs	$ 0.5	$ 73.0