Restructuring - Restructuring Charges By Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 7.4	$ 2.2	$ 11.2	$ 6.1
Severance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	7.3	2.2	11.1	6.1
Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.1	0.0	0.1	0.0
Eurasia Banking | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	1.3	1.2	2.8	3.7
Americas Banking | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.2	0.2	0.6	0.3
Americas Banking | Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0.1	0.0	0.1	0.0
Retail | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	2.8	0.3	3.6	0.8
Corporate | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring charges	3.0	0.5	4.1	1.3
DN2020 Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges		$ 2.2		6.0
Strategic Alliance Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges				$ 0.1
DN Now [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 7.4		$ 11.2