Related Party Transactions - Income Statement Disclosures (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014		Jun. 30, 2013
Related Party Transaction [Line Items]
Income	$ 11.8	$ 4.9	$ 22.8		$ 12.7
Expense incurred	11.8	21.1	25.4		51.5
NN Group
Related Party Transaction [Line Items]
Income	0.6	0.5	1.2	[1]	0.9	[1]
Expense incurred	0.2	2.3	0.3	[1]	5.6	[1]
ING Group
Related Party Transaction [Line Items]
Income	1.3	1.0	6.9		5.2
Expense incurred	3.9	4.6	7.4		9.6
ING Bank N.V.
Related Party Transaction [Line Items]
Income	4.6	(1.0)	4.1	[1]	(1.4)	[1]
Expense incurred	4.1	10.4	10.7	[1]	28.8	[1]
Other
Related Party Transaction [Line Items]
Income	5.3	4.4	10.6		8.0
Expense incurred	$ 3.6	$ 3.8	$ 7.0		$ 7.5

[1] See "Derivatives" section below.