Related Party Transactions - Income Statement Disclosures (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Income	$ 25.2	$ 39.5	$ 35.1
Expense	12.2	49.1	78.2
NN Group
Related Party Transaction [Line Items]
Income	0.4	2.5	1.9
Expense	0.1	0.6	6.1
ING Group
Related Party Transaction [Line Items]
Income	2.8	11.8	7.4
Expense	3.0	14.7	18.0
ING Bank N.V.
Related Party Transaction [Line Items]
Income	18.2	5.6	7.2
Expense	5.7	19.8	39.5
Other
Related Party Transaction [Line Items]
Income	3.8	19.6	18.6
Expense	$ 3.4	$ 14.0	$ 14.6