Related Party Transactions - Balance Sheet Disclosures (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Assets	$ 21.9	$ 18.2
Liabilities	6.9	8.9
NN Group
Related Party Transaction [Line Items]
Assets	0.9	0.5
Liabilities	0.3	0.2
ING Group
Related Party Transaction [Line Items]
Assets	5.7	1.3
Liabilities	1.0	0.9
ING Bank N.V.
Related Party Transaction [Line Items]
Assets	11.8	13.8
Liabilities	3.7	5.8
Other
Related Party Transaction [Line Items]
Assets	3.5	2.6
Liabilities	$ 1.9	$ 2.0