Investments - OTTI (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 securities		Mar. 31, 2013 securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	$ 0.9		$ 0.6
No. of Securities	15		22
U.S. corporate
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	0.1		0
No. of Securities	1		0
Residential mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	0.7		0.5
No. of Securities	11		20
Commercial mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	0.1		0.1
No. of Securities	2		2
Other asset-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	0	[1]	0
No. of Securities	1		0
Intent related impairment
Available-for-sale Securities Including Securities Pledged [Line Items]
No. of Securities	2		2
Write-down related to intent impairments	0.1		0.1
Intent related impairment | U.S. corporate
Available-for-sale Securities Including Securities Pledged [Line Items]
No. of Securities	0		0
Write-down related to intent impairments	0		0
Intent related impairment | Residential mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
No. of Securities	0		0
Write-down related to intent impairments	0		0
Intent related impairment | Commercial mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
No. of Securities	2		2
Write-down related to intent impairments	0.1		0.1
Intent related impairment | Other asset-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
No. of Securities	0		0
Write-down related to intent impairments	0		0
Credit related impairment
Available-for-sale Securities Including Securities Pledged [Line Items]
Write-downs related to credit impairments	$ 0.8		$ 0.5

[1] Less than $0.1.