Investments - Mortgage Loans (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Financing Receivable, Recorded Investment, 1 to 30 Days Past Due	$ 0		$ 0
Maximum loan to value ratio generally allowed	75.00%
Commercial mortgage loans	9,261.5	[1]	9,316.0	[1]
Collective valuation allowance	(3.4)		(3.8)
Total net commercial mortgage loans	9,258.1		9,312.2
Impairments on mortgage loans	0		0
Financing Receivable, Recorded Investment, 31 to 90 Days Past Due	0		5.1
Financing Receivable, Recorded Investment, 91 to 180 Days Past Due	0		0
Financing Receivable, Recorded Investment, Equal to Greater than 181 Days Past Due	0		0
Financing Receivable, Recorded Investment, Past Due	$ 0		$ 5.1

[1] Balances do not include allowance for mortgage loan credit losses.