Investments Composition of US and Foreign Corporate Securities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Sep. 30, 2011
Communications
Available-for-sale Securities, Including Securities Pledged [Line Items]
U.S. and foreign securities, Amortized Cost	$ 1,010.9	$ 1,109.9
U.S. and foreign corporate securities, Gross Unrealized Capital Gains	135.9	96.0
U.S. and foreign corporate securities, Gross Unrealized Capital Losses	0.8	5.3
Fixed maturities, including securities pledged, Fair Value	1,146.0	1,200.6
Financial
Available-for-sale Securities, Including Securities Pledged [Line Items]
U.S. and foreign securities, Amortized Cost	1,681.7	1,948.2
U.S. and foreign corporate securities, Gross Unrealized Capital Gains	167.9	115.1
U.S. and foreign corporate securities, Gross Unrealized Capital Losses	22.7	54.3
Fixed maturities, including securities pledged, Fair Value	1,826.9	2,009.0
Industrial and Other Companies
Available-for-sale Securities, Including Securities Pledged [Line Items]
U.S. and foreign securities, Amortized Cost	8,391.8	8,453.1
U.S. and foreign corporate securities, Gross Unrealized Capital Gains	863.3	634.0
U.S. and foreign corporate securities, Gross Unrealized Capital Losses	8.0	33.2
Fixed maturities, including securities pledged, Fair Value	9,247.1	9,053.9
Utilities
Available-for-sale Securities, Including Securities Pledged [Line Items]
U.S. and foreign securities, Amortized Cost	2,605.7	2,589.6
U.S. and foreign corporate securities, Gross Unrealized Capital Gains	315.3	244.5
U.S. and foreign corporate securities, Gross Unrealized Capital Losses	16.5	10.5
Fixed maturities, including securities pledged, Fair Value	2,904.5	2,823.6
Transportation
Available-for-sale Securities, Including Securities Pledged [Line Items]
U.S. and foreign securities, Amortized Cost	354.5	366.3
U.S. and foreign corporate securities, Gross Unrealized Capital Gains	43.0	31.7
U.S. and foreign corporate securities, Gross Unrealized Capital Losses	0.1	2.5
Fixed maturities, including securities pledged, Fair Value	397.4	395.5
U.S. and Foreign Corporate Securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
U.S. and foreign securities, Amortized Cost	14,044.6	14,467.1
U.S. and foreign corporate securities, Gross Unrealized Capital Gains	1,525.4	1,121.3
U.S. and foreign corporate securities, Gross Unrealized Capital Losses	48.1	105.8
Fixed maturities, including securities pledged, Fair Value	$ 15,521.9	$ 15,482.6