Contingencies, Guarantees, Indemnifications and Leases - Leases (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Assets
Operating lease assets	$ 195.2	$ 195.2
Finance lease assets	32.8	32.8
Total lease assets	228.0	228.0
Liabilities
Operating lease liabilities	204.4	204.4
Finance lease liabilities	33.0	33.0
Total lease liabilities	237.4	237.4
Finance lease cost:
Amortization of right-of-use assets	3.5	7.0
Interest on lease liabilities	0.2	0.5
Operating lease cost	14.4	27.8
Other lease cost	1.8	4.6
Sublease income	(0.4)	(0.8)
Total lease cost	19.5	39.1
Operating leases, payments due for the twelve months ending June 30:
2020	52.5	52.5
2021	45.4	45.4
2022	35.3	35.3
2023	28.0	28.0
2024	17.7	17.7
2025 and thereafter	50.8	50.8
Total lease payments	229.7	229.7
Less: interest	25.3	25.3
Present value of lease liabilities	204.4	204.4
Finance leases, payments due for the twelve months ending June 30:
2020	14.4	14.4
2021	11.5	11.5
2022	6.7	6.7
2023	1.3	1.3
2024	0.2	0.2
2025 and thereafter	0.2	0.2
Total lease payments	34.3	34.3
Less: interest	1.3	1.3
Present value of lease liabilities	33.0	33.0
Total leases, payments due for the twelve months ending June 30:
2020	66.9	66.9
2021	56.9	56.9
2022	42.0	42.0
2023	29.3	29.3
2024	17.9	17.9
2025 and thereafter	51.0	51.0
Total lease payments	264.0	264.0
Less: interest	26.6	26.6
Present value of lease liabilities	$ 237.4	$ 237.4
Weighted-average remaining lease term and weighted-average discount rates
Weighted average remaining lease term, Operating leases	6 years 10 months 24 days	6 years 10 months 24 days
Weighted average remaining lease term, Finance leases	2 years 8 months 12 days	2 years 8 months 12 days
Weighted-average discount rate, Operating leases	4.00%	4.00%
Weighted-average discount rate, Finance leases	2.90%	2.90%