Investments Unrealized Capital Losses 1 (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Available-for-sale Securities Including Securities Pledged [Line Items]
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	$ 21.6	$ 45.5
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	9.8	16.6
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	72.9	91.3
Total Unrealized Capital Losses	104.3	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	1,052.0	1,197.2
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	21.0	46.9
Six months or less below amortized cost, Number of Securities	173	256
More than six months and twelve months or less below amortized cost, Amortized Cost	244.6	270.3
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	10.3	13.9
More than six months and twelve months or less below amortized cost, Number of Securities	58	52
More than twelve months below amortized cost, Amortized Cost	298.5	355.6
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	15.4	26.7
More than twelve months below amortized cost, Number of Securities	109	129
Total Amortized Cost	1,595.1	1,823.1
Total Unrealized Capital Losses	46.7	87.5
More than twelve months below amortized cost, Number of Securities	340	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	25.1	60.1
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	9.9	16.9
Six months or less below amortized cost, Number of Securities	17	31
More than six months and twelve months or less below amortized cost, Amortized Cost	25.9	25.1
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	9.6	9.1
More than six months and twelve months or less below amortized cost, Number of Securities	11	9
More than twelve months below amortized cost, Amortized Cost	110.1	103.9
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	38.1	39.9
More than twelve months below amortized cost, Number of Securities	42	37
Total Amortized Cost	161.1	189.1
Total Unrealized Capital Losses	57.6	65.9
More than twelve months below amortized cost, Number of Securities	70	77
U.S. Treasuries
Available-for-sale Securities Including Securities Pledged [Line Items]
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	0	0
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	0	0
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	0	0
Total Unrealized Capital Losses	0	0
U.S. Treasuries | Fair value decline below amortized cost less than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Amortized Cost	209.1	0
Total Unrealized Capital Losses	0	0
More than twelve months below amortized cost, Number of Securities	3	0
U.S. Treasuries | Fair value decline below amortized cost greater than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Amortized Cost	0	0
Total Unrealized Capital Losses	0	0
More than twelve months below amortized cost, Number of Securities	0	0
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	10.4	22.8
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	5.1	3.0
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	8.4	5.3
Total Unrealized Capital Losses	23.9	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	579.6	717.7
Total Unrealized Capital Losses	15.7	28.8
More than twelve months below amortized cost, Number of Securities	104	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	17.5	7.9
Total Unrealized Capital Losses	8.2	2.3
More than twelve months below amortized cost, Number of Securities	4	3
Foreign
Available-for-sale Securities Including Securities Pledged [Line Items]
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	8.1	19.1
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	3.9	4.6
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	11.0	17.8
Total Unrealized Capital Losses	23.0	41.5
Foreign | Fair value decline below amortized cost less than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Amortized Cost	449.1	670.5
Total Unrealized Capital Losses	14.1	31.9
More than twelve months below amortized cost, Number of Securities	70	122
Foreign | Fair value decline below amortized cost greater than 20%
Available-for-sale Securities Including Securities Pledged [Line Items]
Total Amortized Cost	26.9	25.7
Total Unrealized Capital Losses	8.9	9.6
More than twelve months below amortized cost, Number of Securities	6	7
Residential mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	2.6	1.6
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	0.7	5.2
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	35.5	46.1
Total Unrealized Capital Losses	38.8	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	239.7	276.5
Total Unrealized Capital Losses	10.7	19.0
More than twelve months below amortized cost, Number of Securities	126	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	83.7	98.2
Total Unrealized Capital Losses	28.1	33.9
More than twelve months below amortized cost, Number of Securities	45	47
Commercial mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Six Months or Less Below Amortized Cost, Unrealized Capital Loss	0.4	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	1.0	1.5
Total Unrealized Capital Losses	1.4	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	73.4	110.1
Total Unrealized Capital Losses	1.4	5.4
More than twelve months below amortized cost, Number of Securities	14	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	0.1	0.2
More Than Six Months and Twelve Months or Less Below Amortized Cost, Unrealized Capital Loss	0.1	1.3
More Than Twelve Months Below Amortized Cost, Unrealized Capital Loss	17.0	20.6
Total Unrealized Capital Losses	17.2	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	44.2	48.3
Total Unrealized Capital Losses	4.8	2.4
More than twelve months below amortized cost, Number of Securities	23	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	33.0	55.4
Total Unrealized Capital Losses	$ 12.4	$ 19.7
More than twelve months below amortized cost, Number of Securities	15	19