Goodwill and Other Assets (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Goodwill	$ 1,231.5	$ 1,271.3	$ 1,234.9
Accumulated impairment losses	(470.9)	(470.9)	(470.9)
Beginning balance	800.4	764.0
Transferred to assets held for sale		(1.4)
Divestitures	(0.3)	(10.0)
Currency translation adjustment	(39.5)	47.8
Ending balance	760.6	800.4
Eurasia Banking
Goodwill [Line Items]
Goodwill	569.0	590.4	579.2
Accumulated impairment losses	(291.7)	(291.7)	(291.7)
Beginning balance	298.7	287.5
Transferred to assets held for sale		(1.4)
Divestitures	0.0	(6.4)
Currency translation adjustment	(21.4)	19.0
Ending balance	277.3	298.7
Americas Banking
Goodwill [Line Items]
Goodwill	441.3	444.7	431.3
Accumulated impairment losses	(122.0)	(122.0)	(122.0)
Beginning balance	322.7	309.3
Transferred to assets held for sale		0.0
Divestitures	0.0	(2.4)
Currency translation adjustment	(3.4)	15.8
Ending balance	319.3	322.7
Retail
Goodwill [Line Items]
Goodwill	221.2	236.2	224.4
Accumulated impairment losses	(57.2)	(57.2)	$ (57.2)
Beginning balance	179.0	167.2
Transferred to assets held for sale		0.0
Divestitures	(0.3)	(1.2)
Currency translation adjustment	(14.7)	13.0
Ending balance	$ 164.0	$ 179.0

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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