Restructuring - Restructuring Charges By Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Restructuring Cost and Reserve [Line Items]
Document Period End Date			Jun. 30, 2018
Restructuring Charges	$ 2.2	$ 14.4	$ 6.1	$ 27.3
Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	107.2		107.2
Restructuring Charges	2.2	14.4	6.1	27.3
Eurasia Banking | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	60.2		60.2
Restructuring Charges	1.2	3.1	3.7	9.1
Americas Banking | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	13.8		13.8
Restructuring Charges	0.2	4.0	0.3	3.4
Retail | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	16.3		16.3
Restructuring Charges	0.3	8.5	0.8	9.7
Corporate | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	16.9		16.9
Restructuring Charges	0.5	(1.2)	1.3	$ 5.1
DN2020 Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	2.2	$ 14.4	6.0
DN2020 Plan [Member] | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	95.8		95.8
DN2020 Plan [Member] | Eurasia Banking | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	51.5		51.5
DN2020 Plan [Member] | Americas Banking | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	13.6		13.6
DN2020 Plan [Member] | Retail | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	15.6		15.6
DN2020 Plan [Member] | Corporate | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	15.1		15.1
Delta Program [Member] | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	3.2		3.2
Delta Program [Member] | Eurasia Banking | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	0.5		0.5
Delta Program [Member] | Americas Banking | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	0.2		0.2
Delta Program [Member] | Retail | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	0.7		0.7
Delta Program [Member] | Corporate | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	1.8		1.8
Strategic Alliance Plan [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges			0.1
Strategic Alliance Plan [Member] | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	8.2		8.2
Strategic Alliance Plan [Member] | Eurasia Banking | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	8.2		8.2
Strategic Alliance Plan [Member] | Americas Banking | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	0.0		0.0
Strategic Alliance Plan [Member] | Retail | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	0.0		0.0
Strategic Alliance Plan [Member] | Corporate | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Cost Incurred to Date	$ 0.0		$ 0.0