Investments - OTTI (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 security	Mar. 31, 2013 security
Available-for-sale Securities, Including Securities Pledged [Line Items]
Impairment	$ 3.3	$ 11.0
No. of Securities	44	78
U.S. corporate securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Impairment	0.4	0
No. of Securities	1	0
Residential mortgage-backed
Available-for-sale Securities, Including Securities Pledged [Line Items]
Impairment	1.6	3.6
No. of Securities	37	74
Commercial mortgage-backed
Available-for-sale Securities, Including Securities Pledged [Line Items]
Impairment	0.2	0.1
No. of Securities	2	2
Other asset-backed securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Impairment	0.1	7.3
No. of Securities	2	2
Equity securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Impairment	1.0	0
No. of Securities	2	0
Intent related impairment
Available-for-sale Securities, Including Securities Pledged [Line Items]
No. of Securities	2	4
Write-down related to intent impairments	0.2	7.4
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	0.2	0.1
Intent related impairment | Other asset-backed securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
No. of Securities	0	2
Write-down related to intent impairments	0	7.3
Credit related impairment
Available-for-sale Securities, Including Securities Pledged [Line Items]
Write-downs related to credit impairments	$ 3.1	$ 3.6