Related Party Transactions - Balance Sheet Disclosures (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Assets	$ 23.0	$ 18.2
Liabilities	5.8	8.9
NN Group
Related Party Transaction [Line Items]
Assets	0.5	0.5
Liabilities	0.1	0.2
ING Group
Related Party Transaction [Line Items]
Assets	9.0	1.3
Liabilities	0.9	0.9
ING Bank N.V.
Related Party Transaction [Line Items]
Assets	11.1	13.8
Liabilities	3.2	5.8
Other
Related Party Transaction [Line Items]
Assets	2.4	2.6
Liabilities	$ 1.6	$ 2.0