Investments Composition of US and Foreign Corporate Securities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Communications
Available-for-sale Securities Including Securities Pledged [Line Items]
U.S. and foreign securities, Amortized Cost	$ 1,315.9	$ 1,154.1
U.S. and foreign corporate securities, Gross Unrealized Capital Gains	81.5	161.4
U.S. and foreign corporate securities, Gross Unrealized Capital Losses	36.8	0.9
Fixed maturities, including securities pledged, Fair Value	1,360.6	1,314.6
Financial
Available-for-sale Securities Including Securities Pledged [Line Items]
U.S. and foreign securities, Amortized Cost	2,114.7	1,859.3
U.S. and foreign corporate securities, Gross Unrealized Capital Gains	166.9	240.1
U.S. and foreign corporate securities, Gross Unrealized Capital Losses	20.2	10.9
Fixed maturities, including securities pledged, Fair Value	2,261.4	2,088.5
Industrial and Other Companies
Available-for-sale Securities Including Securities Pledged [Line Items]
U.S. and foreign securities, Amortized Cost	8,878.5	7,883.1
U.S. and foreign corporate securities, Gross Unrealized Capital Gains	423.5	850.9
U.S. and foreign corporate securities, Gross Unrealized Capital Losses	213.1	6.9
Fixed maturities, including securities pledged, Fair Value	9,088.9	8,727.1
Utilities
Available-for-sale Securities Including Securities Pledged [Line Items]
U.S. and foreign securities, Amortized Cost	2,726.5	2,715.4
U.S. and foreign corporate securities, Gross Unrealized Capital Gains	159.5	349.8
U.S. and foreign corporate securities, Gross Unrealized Capital Losses	42.3	7.3
Fixed maturities, including securities pledged, Fair Value	2,843.7	3,057.9
Transportation
Available-for-sale Securities Including Securities Pledged [Line Items]
U.S. and foreign securities, Amortized Cost	440.0	396.1
U.S. and foreign corporate securities, Gross Unrealized Capital Gains	22.5	46.5
U.S. and foreign corporate securities, Gross Unrealized Capital Losses	9.9	0.4
Fixed maturities, including securities pledged, Fair Value	452.6	442.2
U.S. and Foreign Corporate Securities
Available-for-sale Securities Including Securities Pledged [Line Items]
U.S. and foreign securities, Amortized Cost	15,475.6	14,008.0
U.S. and foreign corporate securities, Gross Unrealized Capital Gains	853.9	1,648.7
U.S. and foreign corporate securities, Gross Unrealized Capital Losses	322.3	26.4
Fixed maturities, including securities pledged, Fair Value	$ 16,007.2	$ 15,630.3