Common Share Repurchases (details) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2016 USD ($) $ / shares shares	Jun. 30, 2016 USD ($) $ / shares shares
Common Share Repurchases disclosure
Number of shares repurchased (in shares) | shares	4,900,000	10,000,000
Cost of shares repurchased	$ 550.0	$ 1,100.0
Average cost per share repurchased | $ / shares	$ 112.12	$ 110.26
Remaining capacity under share repurchase authorization	$ 2,230.0	$ 2,230.0
Number of shares acquired to cover tax withholding costs and exercise costs (in shares) | shares	5,146	500,000
Cost of shares acquired to cover tax withholding costs and exercise costs	$ 0.6	$ 59.0