Business Segments, Geographic Information and Major Customers - Geographic Summary (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Revenue	$ 9,358.1	$ 9,322.7	$ 9,459.4	$ 8,678.8	$ 9,988.6	$ 10,429.5	$ 10,150.8	$ 9,181.3	$ 36,819.0	$ 39,750.3	$ 33,695.5
Property and equipment, net:
Property and equipment, net	360.9								360.9
Property and equipment, net					350.3					350.3
United States
Revenue:
Revenue									19,365.2	20,555.5	17,938.0
Property and equipment, net:
Property and equipment, net	173.0								173.0
Property and equipment, net					175.1					175.1
EMEA
Revenue:
Revenue									9,235.1	9,721.9	7,553.3
Property and equipment, net:
Property and equipment, net	135.7								135.7
Property and equipment, net					124.5					124.5
Asia Pacific
Revenue:
Revenue									4,581.1	5,537.2	4,923.0
Property and equipment, net:
Property and equipment, net	44.2								44.2
Property and equipment, net					7.5					7.5
Americas, excluding United States
Revenue:
Revenue									3,637.6	3,935.6	3,281.2
Property and equipment, net:
Property and equipment, net	$ 8.0								8.0
Property and equipment, net					$ 43.1					43.1
U.K.
Revenue:
Revenue									5,500.0	6,300.0	5,000.0
Singapore
Revenue:
Revenue									$ 4,500.0	$ 5,400.0	$ 4,800.0