Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Tax Act, provisional income tax expense		$ 106.3
Tax Act, income tax expense	$ 28.9	106.3	$ 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, provisional net cash liability, transition tax on accumulated foreign earnings		102.9
Tax Act, net cash liability, transition tax on accumulated foreign earnings	139.1
Income tax expense, dividends withholding tax on repatriation of foreign earnings	3.0	87.5
Income tax expense, GILTI	12.9
Income Before Income Taxes [Abstract]
Income before income taxes, Domestic	643.7	832.4	805.2
Income before income taxes, International	1,280.6	1,052.5	1,036.6
Income Before Income Taxes and Income From Equity Method Investments	1,924.3	1,884.9	1,841.8
Income Tax Expense [Abstract]
Income tax expense, current, Federal	273.8	458.8	381.8
Income tax expense, current, State and local	35.5	36.5	12.6
Income tax expense, current, International	305.2	280.2	332.1
Income tax expense, current	614.5	775.5	726.5
Income tax expense, deferred, Federal	(104.2)	(205.5)	(88.2)
Income tax expense, deferred, State and local	2.8	11.1	12.0
Income tax expense, deferred, International	(20.4)	115.1	(49.8)
Income tax expense, deferred	(121.8)	(79.3)	(126.0)
Income tax expense	$ 492.7	$ 696.2	$ 600.5
Reconciliation from the Statutory U.S. Federal Income Tax Rate to Effective Tax Rate [Abstract]
Statutory U.S. federal income tax rate	21.00%	35.00%	35.00%
State and local income taxes, net of federal income tax benefit	1.50%	1.30%	0.90%
Effect of Tax Act	1.60%	5.60%	0.00%
International tax rate differentials	1.10%	(3.80%)	(4.00%)
Other	0.40%	(1.20%)	0.70%
Effective tax rate	25.60%	36.90%	32.60%
Income tax expense reduction, resolution of foreign tax claims	$ (19.0)
Unrecognized Tax Benefits, Penalties and Interest [Abstract]
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	3.6	$ 2.5	$ 2.3
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	21.1	16.1
Deferred tax assets:
Compensation	209.7	173.7
Tax loss and credit carryforwards	38.1	40.3
Basis differences from acquisitions	13.9	18.0
Basis differences from short-term assets and liabilities	35.7	39.5
Other	10.8	17.8
Deferred tax assets	308.2	289.3
Valuation allowance	(3.0)	(3.3)
Net deferred tax assets	305.2	286.0
Deferred tax liabilities:
Goodwill and intangible assets	577.5	562.2
Unremitted foreign earnings	69.2	94.9
Basis differences from investments	9.6	9.8
Financial instruments	0.8	41.4
Deferred tax liabilities	657.1	708.3
Long-term deferred tax assets	61.8	61.3
Long-term deferred tax liabilities	413.7	483.6
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
January 1	173.7	116.9
Current year tax positions	30.1	67.1
Prior year tax positions	5.2	5.5
Reduction of prior year tax positions	(25.4)	(16.5)
Foreign currency translation		0.7
Foreign currency translation	(0.8)
December 31	182.8	173.7	$ 116.9
Unrecognized tax benefits that would impact effective tax rate	$ 174.0	$ 142.8
Minimum [Member]
Deferred tax liabilities:
Tax loss and credit carryforwards, expiration dates	Dec. 31, 2019
Maximum [Member]
Deferred tax liabilities:
Tax loss and credit carryforwards, expiration dates	Dec. 31, 2038