Income Taxes - Narrative (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Nov. 18, 2014	Sep. 08, 2014	Mar. 25, 2014	Oct. 29, 2013
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would affect effective rate	$ 14.1	$ 14.1	$ 16.1	$ 19.7
Valuation allowance	971.9	971.9	2,821.9
Loss related to sale of certain businesses	(107.0)	(157.3)	(59.8)	(45.8)
Net actuarial (gains) losses	(372.7)	(372.7)	405.2	(165.0)
Valuation allowance, deferred tax asset, increase (decrease) in amount		(1,850.0)	(152.2)	99.1
Accrued interest and penalties related to unrecognized tax	7.0	7.0	6.2
Interest (benefit) recognized related to unrecognized tax		0.8	0.3	(17.3)
Unrecognized Tax Benefits	14.0	14.0
Unrecognized Tax Benefits	62.4	62.4	60.9	61.1	74.0
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits	10.2	10.2	10.2
Valuation allowance on deferred tax assets
Income Tax Contingency [Line Items]
Increase (decrease) in valuation allowance allocated to operations	1,640.0	(1,850.0)	(86.6)	99.1
Valuation Allowances and Reserves, Deductions		0	65.6	0
Increase (decrease) in the valuation allowance allocated to operations that impacted income tax expense				(48.3)
Increase (decrease) in the valuation allowance allocated to operations that did not impact income tax expense				147.4
Valuation allowance on deferred tax assets
Income Tax Contingency [Line Items]
Valuation allowance	1,000.0	1,000.0	2,800.0
Deferred Tax Asset, Operating Loss Carryforward
Income Tax Contingency [Line Items]
Valuation allowance	1,300.0	1,300.0	3,200.0
Deferred Tax Asset, Capital Loss Carryforward
Income Tax Contingency [Line Items]
Valuation allowance	354.1	354.1	(354.1)
Payment of Allowance
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits	$ 48.4	$ 48.4
ING Group
Income Tax Contingency [Line Items]
Ownership by affiliate of parent company	20.00%	20.00%				19.00%	32.50%	43.00%	57.00%