Restructuring - Restructuring Charges By Plan (Details) $ in Millions	Dec. 31, 2019 USD ($)
Severance
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	$ 213.1
Severance | Eurasia Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	106.5
Severance | Americas Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	24.1
Severance | Retail Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	37.8
Severance | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	44.7
Severance | DN Now Plan [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	109.0
Severance | DN Now Plan [Member] | Eurasia Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	46.8
Severance | DN Now Plan [Member] | Americas Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	10.4
Severance | DN Now Plan [Member] | Retail Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	22.2
Severance | DN Now Plan [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	29.6
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 | 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 | DN Now Plan [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	0.1
Other Restructuring | DN Now Plan [Member] | Eurasia Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	0.0
Other Restructuring | DN Now Plan [Member] | Americas Banking Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	0.1
Other Restructuring | DN Now Plan [Member] | Retail Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	0.0
Other Restructuring | DN Now Plan [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred to date	$ 0.0