Income Taxes - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Decrease in valuation allowance	$ 30.0
Adjustment to additional paid-in-capital for income tax benefits attributable to employee stock compensation	126.0	$ 89.0	$ 74.0
Deferred tax liabilities from undistributed foreign earnings	20.0
Undistributed foreign earnings	2,200.0
Benefit realized from tax holiday granted	$ 23.0	$ 7.0	$ 3.0
Earnings per share impact of tax holiday	$ 0.08	$ 0.02	$ 0.01
Unrecognized tax benefits that would impact effective tax rate	$ 180.0	$ 154.0	$ 141.0
Accrued potential interest and penalties	2.0	4.0	2.0
Liability recorded for interest and penalties	33.0	31.0	$ 27.0
U.K. [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	449.0	154.0
Capital loss carryforwards	360.0	380.0
U.S. Federal [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	7.5	18.0
U.S. State [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	443.0	451.0
Other [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	245.0	325.0
Capital loss carryforwards	$ 206.0	$ 223.0