Restructuring - Restructuring Charges By Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	$ 0.0	$ 13.8	$ 23.1	$ 35.3
Severance
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.0	13.8	10.3	35.3
Severance | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.0	2.5	0.0	6.0
Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.0		12.8	0.0
Eurasia Banking | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.0	8.6	8.8	16.7
Eurasia Banking | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.0		0.6	0.0
Americas Banking | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.0	0.7	0.3	1.8
Retail | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.0	$ 2.0	1.2	10.8
Retail | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.0		1.6	0.0
Corporate and Other | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	0.0		10.6	$ 0.0
DN Now [Member] | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	195.1		195.1
DN Now [Member] | Severance | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	54.3		54.3
DN Now [Member] | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	18.7		18.7
DN Now [Member] | Other Restructuring [Member] | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	12.2		12.2
DN Now [Member] | Eurasia Banking | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	87.7		87.7
DN Now [Member] | Eurasia Banking | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	2.6		2.6
DN Now [Member] | Americas Banking | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	13.2		13.2
DN Now [Member] | Americas Banking | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	0.1		0.1
DN Now [Member] | Retail | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	39.9		39.9
DN Now [Member] | Retail | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	$ 3.8		$ 3.8