Investments Unrealized Capital Losses 1 (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Available-for-sale Securities Including Securities Pledged [Line Items]
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	$ 6.4	$ 45.5
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	7.3	16.6
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	49.4	91.3
Total Unrealized Capital Losses	63.1	153.4
Fair value decline below amortized cost less than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Six months or less below amortized cost, Amortized Cost	360.1	1,197.2
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	14.8	46.9
Six months or less below amortized cost, Number of Securities	86	256
More than six months and twelve months or less below amortized cost, Amortized Cost	101.7	270.3
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	6.7	13.9
More than six months and twelve months or less below amortized cost, Number of Securities	48	52
More than twelve months below amortized cost, Amortized Cost	205.5	355.6
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	8.6	26.7
More than twelve months below amortized cost, Number of Securities	92	129
Total Amortized Cost	667.3	1,823.1
Total Unrealized Capital Losses	30.1	87.5
More than twelve months below amortized cost, Number of Securities	226	437
Fair value decline below amortized cost greater than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Six months or less below amortized cost, Amortized Cost	21.8	60.1
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	5.5	16.9
Six months or less below amortized cost, Number of Securities	13	31
More than six months and twelve months or less below amortized cost, Amortized Cost	5.5	25.1
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	2.4	9.1
More than six months and twelve months or less below amortized cost, Number of Securities	4	9
More than twelve months below amortized cost, Amortized Cost	68.2	103.9
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	25.1	39.9
More than twelve months below amortized cost, Number of Securities	29	37
Total Amortized Cost	95.5	189.1
Total Unrealized Capital Losses	33.0	65.9
More than twelve months below amortized cost, Number of Securities	46	77
U.S. corporate, state and municipalities
Available-for-sale Securities Including Securities Pledged [Line Items]
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	1.9	22.8
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	3.6	3.0
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	5.5	5.3
Total Unrealized Capital Losses	11.0	31.1
U.S. corporate, state and municipalities | Fair value decline below amortized cost less than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Amortized Cost	221.1	717.7
Total Unrealized Capital Losses	7.5	28.8
More than twelve months below amortized cost, Number of Securities	55	119
U.S. corporate, state and municipalities | Fair value decline below amortized cost greater than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Amortized Cost	6.1	7.9
Total Unrealized Capital Losses	3.5	2.3
More than twelve months below amortized cost, Number of Securities	2	3
Foreign
Available-for-sale Securities Including Securities Pledged [Line Items]
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	4.1	19.1
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	2.2	4.6
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	13.4	17.8
Total Unrealized Capital Losses	19.7	41.5
Foreign | Fair value decline below amortized cost less than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Amortized Cost	162.6	670.5
Total Unrealized Capital Losses	7.1	31.9
More than twelve months below amortized cost, Number of Securities	25	122
Foreign | Fair value decline below amortized cost greater than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Amortized Cost	40.3	25.7
Total Unrealized Capital Losses	12.6	9.6
More than twelve months below amortized cost, Number of Securities	10	7
Residential mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	0.4	1.6
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	1.5	5.2
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	20.2	46.1
Total Unrealized Capital Losses	22.1	52.9
Residential mortgage-backed | Fair value decline below amortized cost less than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Amortized Cost	225.3	276.5
Total Unrealized Capital Losses	11.4	19.0
More than twelve months below amortized cost, Number of Securities	121	119
Residential mortgage-backed | Fair value decline below amortized cost greater than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Amortized Cost	30.9	98.2
Total Unrealized Capital Losses	10.7	33.9
More than twelve months below amortized cost, Number of Securities	26	47
Commercial mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	0	1.8
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	0	2.5
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	0.2	1.5
Total Unrealized Capital Losses	0.2	5.8
Commercial mortgage-backed | Fair value decline below amortized cost less than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Amortized Cost	8.3	110.1
Total Unrealized Capital Losses	0.2	5.4
More than twelve months below amortized cost, Number of Securities	4	16
Commercial mortgage-backed | Fair value decline below amortized cost greater than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Amortized Cost	0	1.9
Total Unrealized Capital Losses	0	0.4
More than twelve months below amortized cost, Number of Securities	0	1
Other asset-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	0	0.2
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	0	1.3
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	10.1	20.6
Total Unrealized Capital Losses	10.1	22.1
Other asset-backed | Fair value decline below amortized cost less than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Amortized Cost	50.0	48.3
Total Unrealized Capital Losses	3.9	2.4
More than twelve months below amortized cost, Number of Securities	21	61
Other asset-backed | Fair value decline below amortized cost greater than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Amortized Cost	18.2	55.4
Total Unrealized Capital Losses	$ 6.2	$ 19.7
More than twelve months below amortized cost, Number of Securities	8	19