Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended			24 Months Ended	48 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2010	Dec. 31, 2017
Tax Act, provisional income tax expense	$ 106.3	$ 0.0	$ 0.0
Tax Act, provisional income tax benefit, remeasurement of deferred tax assets and liabilities	173.3
Tax Act, provisional income tax expense, transition tax on accumulated foreign earnings	192.1
Tax Act, net cash liability, transition tax on accumulated foreign earnings	102.9				$ 102.9
Income tax expense, dividends withholding tax on repatriation of foreign earnings	87.5
Income Before Income Taxes [Abstract]
Income before income taxes, Domestic	832.4	805.2	803.3
Income before income taxes, International	1,052.5	1,036.6	975.3
Income Before Income Taxes and Income From Equity Method Investments	1,884.9	1,841.8	1,778.6
Income Tax Expense [Abstract]
Income tax expense, current, Federal	458.8	381.8	342.3
Income tax expense, current, State and local	36.5	12.6	29.9
Income tax expense, current, International	280.2	332.1	324.5
Income tax expense, current	775.5	726.5	696.7
Income tax expense, deferred, Federal	(205.5)	(88.2)	(86.7)
Income tax expense, deferred, State and local	11.1	12.0	12.1
Income tax expense, deferred, International	115.1	(49.8)	(38.5)
Income tax expense, deferred	(79.3)	(126.0)	(113.1)
Income tax expense	$ 696.2	$ 600.5	$ 583.6
Reconciliation from the Statutory U.S. Federal Income Tax Rate to Effective Tax Rate [Abstract]
Statutory U.S. federal income tax rate	35.00%	35.00%	35.00%
State and local income taxes, net of federal income tax benefit	1.30%	0.90%	1.50%
Effect of Tax Act	5.60%	0.00%	0.00%
International tax rate differentials	(3.80%)	(4.00%)	(3.70%)
Other	(1.20%)	0.70%	0.00%
Effective tax rate	36.90%	32.60%	32.80%
Unrecognized Tax Benefits, Penalties and Interest [Abstract]
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	$ 2.5	$ 2.3	$ 1.1
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	16.1	11.9			16.1
Deferred tax assets:
Compensation	173.7	307.5			173.7
Tax loss and credit carryforwards	40.3	88.5			40.3
Basis differences from acquisitions	18.0	24.3			18.0
Basis differences from short-term assets and liabilities	39.5	36.2			39.5
Other	17.8	18.7			17.8
Deferred tax assets	289.3	475.2			289.3
Valuation allowance	(3.3)	(3.0)			(3.3)
Net deferred tax assets	286.0	472.2			286.0
Deferred tax liabilities:
Goodwill and intangible assets	562.2	802.7			562.2
Unremitted foreign earnings	94.9	15.9			94.9
Financial instruments	41.4	132.3			41.4
Basis differences from investments	9.8	1.8			9.8
Deferred tax liabilities	708.3	952.7			708.3
Long-term deferred tax assets	61.3	0.0			61.3
Long-term deferred tax liabilities	483.6	480.5			483.6
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
January 1	116.9	113.0
Current year tax positions	67.1	20.0
Prior year tax positions	5.5	6.5
Reduction of prior year tax positions	(16.5)	(21.9)
Settlements	0.0	(0.7)
Foreign currency translation	0.7	0.0
December 31	173.7	116.9	$ 113.0		173.7
Unrecognized tax benefits that would impact effective tax rate	$ 142.8	$ 71.0			142.8
Convertible Debt [Member]
Deferred tax liabilities:
Financial instruments				$ 329.0
Convertible debt, repayments of convertible debt				$ 1,400.0
Taxes paid, cancellation of indebtedness income for debt reacquired					$ 263.0
Minimum [Member]
Deferred tax liabilities:
Tax loss and credit carryforwards, expiration dates	Dec. 31, 2018
Maximum [Member]
Deferred tax liabilities:
Tax loss and credit carryforwards, expiration dates	Dec. 31, 2037