Restructuring - Restructuring Charges By Plan (Details) $ in Millions	Dec. 31, 2018 USD ($)
Severance
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	$ 166.1
Severance | Eurasia Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	93.5
Severance | Americas Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	22.4
Severance | Retail Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	28.8
Severance | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	21.4
Severance | DN Now Plan [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	58.9
Severance | DN Now Plan [Member] | Eurasia Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	33.3
Severance | DN Now Plan [Member] | Americas Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	8.6
Severance | DN Now Plan [Member] | Retail Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	12.5
Severance | DN Now Plan [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	4.5
Severance | Global Realigment Plan
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	105.0
Severance | DN2020 Plan [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	95.8
Severance | DN2020 Plan [Member] | Eurasia Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	51.5
Severance | DN2020 Plan [Member] | Americas Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	13.6
Severance | DN2020 Plan [Member] | Retail Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	15.6
Severance | DN2020 Plan [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	15.1
Severance | Delta Program [Member] [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	3.2
Severance | Delta Program [Member] [Member] | Eurasia Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	0.5
Severance | Delta Program [Member] [Member] | Americas Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	0.2
Severance | Delta Program [Member] [Member] | Retail Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	0.7
Severance | Delta Program [Member] [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	1.8
Severance | Strategic Alliance Plan [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	8.2
Severance | Strategic Alliance Plan [Member] | Eurasia Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	8.2
Severance | Strategic Alliance Plan [Member] | Americas Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	0.0
Severance | Strategic Alliance Plan [Member] | Retail Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	0.0
Severance | Strategic Alliance Plan [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	0.0
Other Restructuring [Member] | Global Realigment Plan
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	$ 3.5