Related Party Transactions - Balance Sheet Disclosures (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Assets	$ 21.0	$ 18.2
Liabilities	6.8	8.9
NN Group
Related Party Transaction [Line Items]
Assets	0.6	0.5
Liabilities	0.2	0.2
ING Group
Related Party Transaction [Line Items]
Assets	2.7	1.3
Liabilities	1.2	0.9
ING Bank N.V.
Related Party Transaction [Line Items]
Assets	14.1	13.8
Liabilities	3.6	5.8
Other
Related Party Transaction [Line Items]
Assets	3.6	2.6
Liabilities	$ 1.8	$ 2.0