Related Party Transactions - Income Statement Disclosures (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Related Party Transaction [Line Items]
Income	$ 10.0	$ 10.9	$ 32.8	$ 23.6
Expense incurred	11.9	13.2	37.3	64.7
NN Group
Related Party Transaction [Line Items]
Income	1.0	0.6	2.2	1.5
Expense incurred	0.1	0.4	0.4	6.0
ING Group
Related Party Transaction [Line Items]
Income	3.9	2.1	10.8	7.3
Expense incurred	3.5	4.1	10.9	13.7
ING Bank N.V.
Related Party Transaction [Line Items]
Income	0.3	3.0	4.4	1.6
Expense incurred	4.7	5.3	15.4	34.1
Other
Related Party Transaction [Line Items]
Income	4.8	5.2	15.4	13.2
Expense incurred	$ 3.6	$ 3.4	$ 10.6	$ 10.9