Goodwill and Other Assets Schedule of Intangible Assets (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 1,035.5		$ 1,085.9
Accumulated amortization	(664.3)		(637.3)
Net carrying amount	371.2		448.6
Payments to Develop Software	21.6	$ 12.1
Amortization of internally-developed software	$ (17.7)	(19.8)
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	4 years 4 months 24 days
Gross carrying amount	$ 719.0		762.0
Accumulated amortization	(391.5)		(354.1)
Net carrying amount	$ 327.5		407.9
Internally-developed software [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	2 years 1 month 6 days
Gross carrying amount	$ 210.8		198.0
Accumulated amortization	(169.3)		(160.0)
Net carrying amount	41.5	37.1	38.0	$ 46.0
Transfer To Held For Sale	$ (0.4)	$ (1.2)
Development costs non-software [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	1 year 4 months 24 days
Gross carrying amount	$ 52.9		56.1
Accumulated amortization	(52.7)		(55.8)
Net carrying amount	$ 0.2		0.3
Other intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life	5 years 10 months 24 days
Gross carrying amount	$ 52.8		69.8
Accumulated amortization	(50.8)		(67.4)
Net carrying amount	2.0		2.4
Other intangible asset, net [Member]
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	316.5		323.9
Accumulated amortization	(272.8)		(283.2)
Net carrying amount	43.7		$ 40.7
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Net carrying amount	$ 327.5