Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lease Cost [Abstract]
Operating lease cost	$ 303.6	$ 317.8
Variable lease cost	28.5	38.2
Short-term lease cost	4.3	4.9
Sublease income	(0.9)	(5.1)
Operating leases, Total lease cost	335.5	355.8
Finance leases, Amortization of ROU assets	50.2	43.2
Finance leases, Interest	5.3	5.1
Finance leases, Total lease cost	55.5	48.3
Total lease cost	391.0	404.1
Rent Expense [Abstract]
Operating leases, third-party sublease rent			$ (7.2)
Operating leases, Total rent cost			304.4
Assets under capital lease, amortization expense			36.7
Balance Sheet Classification and Weighted Average Remaining Lease Term and Weighted Average Discount Rate for Operating and Finance Leases [Abstract]
Operating Lease Right-Of-Use Assets	$ 1,223.4	$ 1,398.3
Operating lease liability, current, balance sheet classification	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent
Operating lease liability, current	$ 270.5	$ 290.3
Long-Term Liability - Operating Leases	1,114.0	1,274.7
Operating lease liability, total	$ 1,384.5	$ 1,565.0
Operating leases, weighted average remaining lease term	7 years 10 months 24 days	8 years 2 months 12 days
Operating leases, weighted average discount rate	3.70%	3.80%
Finance lease right-of-use assets	$ 120.7	$ 138.7
Finance lease liability, current	49.5	46.6
Finance lease liability, long-term	74.6	92.1
Finance lease liability, total	$ 124.1	$ 138.7
Finance leases, weighted average remaining lease term	3 years	3 years 4 months 24 days
Finance leases, weighted average discount rate	4.20%	4.30%
Maturity of Undiscounted Cash Flows for Operating and Finance Leases [Abstract]
Operating Leases Payments, 2021	$ 313.8
Operating Leases Payments, 2022	256.6
Operating Leases Payments, 2023	193.6
Operating Leases Payments, 2024	167.9
Operating Leases Payments, 2025	141.9
Operating Leases Payments, Thereafter	536.2
Operating Leases, Total lease payments	1,610.0
Operating Leases, Less: Imputed interest	225.5
Operating Leases, Present value of lease liability	1,384.5	$ 1,565.0
Finance Leases Payments, 2021	49.7
Finance Leases Payments, 2022	36.7
Finance Leases Payments, 2023	24.2
Finance Leases Payments, 2024	11.9
Finance Leases Payments, 2025	4.1
Finance Leases Payments, Thereafter	3.7
Finance Leases, Total lease payments	130.3
Finance Leases, Less: Imputed interest	6.2
Finance Leases, Present value of lease liability	$ 124.1	$ 138.7
Office [Member]
Rent Expense [Abstract]
Operating leases, rent			295.0
Equipment [Member]
Rent Expense [Abstract]
Operating leases, rent			$ 16.6