Business Combinations (Dyax Assets Acquired and Liabilities Assumed) (Details) - USD ($) $ in Millions	Jan. 22, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Non-current assets:
Goodwill		$ 19,831.7	$ 17,888.2	$ 4,147.8
Dyax
Current assets:
Cash and cash equivalents	$ 241.2
Accounts receivable	22.5
Inventories	20.2
Other current assets	8.1
Total current assets	292.0
Non-current assets:
Property, plant and equipment	5.8
Goodwill	2,702.1
Other non-current assets	28.6
Total assets	7,688.5
Current liabilities:
Accounts payable and accrued expenses	30.0
Other current liabilities	1.7
Deferred tax liability	1,325.4
Other non-current liabilities	1.4
Total liabilities	1,358.5
Fair value of identifiable assets acquired and liabilities assumed	6,330.0
Fair value of purchase consideration	6,330.0
Currently marketed products | Dyax
Non-current assets:
Intangible assets	135.0
In-Process Research and Development (IPR&D) | Dyax
Non-current assets:
Intangible assets	4,100.0
Contract based royalty arrangements | Dyax
Non-current assets:
Intangible assets	$ 425.0