Related Party Transactions - Credit Facilities (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	Dec. 31, 2013
Related Party Transaction [Line Items]
Due to affiliate	$ 6.9		$ 6.9		$ 8.9
Expense incurred	11.9	13.2	37.3	64.7
ING Bank N.V.
Related Party Transaction [Line Items]
Due to affiliate	3.7		3.7		5.8
Expense incurred	4.7	5.3	15.4	34.1
ING Bank N.V. | Senior Unsecured Credit Facility
Related Party Transaction [Line Items]
Due to affiliate	3.7		3.7		4.9
Expense incurred	$ 4.0	$ 4.8	$ 11.5	$ 33.0