Investments - Mortgages by Year of Origination (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Investment [Line Items]
Total Commercial mortgage loans	$ 9,953.1	[1]	$ 9,316.0	[1]
Year of Origination 2014
Investment [Line Items]
Total Commercial mortgage loans	1,494.2	[1]	0	[1]
Year of Origination 2013
Investment [Line Items]
Total Commercial mortgage loans	2,157.9	[1]	2,199.8	[1]
Year of Origination 2012
Investment [Line Items]
Total Commercial mortgage loans	1,706.0	[1]	1,743.3	[1]
Year of Origination 2011
Investment [Line Items]
Total Commercial mortgage loans	1,655.3	[1]	1,835.9	[1]
Year of Origination 2010
Investment [Line Items]
Total Commercial mortgage loans	369.4	[1]	409.8	[1]
Year of Origination 2009
Investment [Line Items]
Total Commercial mortgage loans	86.1	[1]	149.5	[1]
Year of Origination 2008 and prior
Investment [Line Items]
Total Commercial mortgage loans	$ 2,484.2	[1]	$ 2,977.7	[1]

[1] Balances do not include collective valuation allowance for losses.