Investments - OTTI (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014 securities		Jun. 30, 2013 securities		Jun. 30, 2014 securities		Jun. 30, 2013 securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	$ 1.4		$ 1.3		$ 2.3		$ 1.9
No. of Securities	18		21		24		29
U.S. corporate
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	0		0		0.1		0
No. of Securities	0		0		1		0
Foreign
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	1.2	[1]	0	[1]	1.2	[1]	0	[1]
No. of Securities	5	[1]	0	[1]	0	[1]	0	[1]
Residential mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	0.2		1.3		0.9		1.8
No. of Securities	12		21		15		27
Commercial mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	0		0		0.1		0.1
No. of Securities	0		0		2		2
Other asset-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Impairment	0	[2]	0		0	[2]	0
No. of Securities	1		0		1		0
Intent related impairment
Available-for-sale Securities Including Securities Pledged [Line Items]
No. of Securities	7		0		9		2
Write-down related to intent impairments	1.3		0		1.4		0.1
Intent related impairment | U.S. corporate
Available-for-sale Securities Including Securities Pledged [Line Items]
No. of Securities	0		0		0		0
Write-down related to intent impairments	0		0		0		0
Intent related impairment | Foreign
Available-for-sale Securities Including Securities Pledged [Line Items]
No. of Securities	5	[1]	0	[1]	5	[1]	0	[1]
Write-down related to intent impairments	1.2	[1]	0	[1]	1.2	[1]	0	[1]
Intent related impairment | Residential mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
No. of Securities	2		0		2		0
Write-down related to intent impairments	0.1		0		0.1		0
Intent related impairment | Commercial mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
No. of Securities	0		0		2		2
Write-down related to intent impairments	0		0		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		0		0
Write-down related to intent impairments	0		0		0		0
Credit related impairment
Available-for-sale Securities Including Securities Pledged [Line Items]
Write-downs related to credit impairments	$ 0.1		$ 1.3		$ 0.9		$ 1.8

[1] Primarily U.S. dollar denominated.

[2] Less than $0.1.