Fair Value Of Assets And Liabilities (Fair Value Of Financial Instruments Held By Consolidated Investments) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash and cash equivalents	$ 1,174.5	$ 835.5	$ 880.1	$ 835.5	$ 727.4
Foreign time deposits	29.6	31.3
Assets held for policyholders	1,449.0	1,153.6
Policyholder payables	(1,449.0)	(1,153.6)
Total debt	(1,387.6)	(1,186.0)
Estimate of Fair Value, Fair Value Disclosure [Member]
Cash and cash equivalents		835.5
Available for sale investments	134.3	122.1
Trading investments	242.5	218.7
Foreign time deposits		31.3
Assets held for policyholders		1,153.6
Support agreements	0	(1.0)
Policyholder payables	(1,449.0)	(1,153.6)
Option contracts	0	0
UIT-related financial instruments sold, not yet purchased	(2.0)	(1.5)
Note payable	(1.2)	(3.4)
Total debt	(1,343.1)	(1,204.8)
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Cash and cash equivalents		835.5
Available for sale investments	134.3	122.1
Trading investments		218.7
Foreign time deposits		31.3
Assets held for policyholders		1,153.6
Support agreements	0	(1.0)
Policyholder payables	(1,449.0)	(1,153.6)
Option contracts	0	0
UIT-related financial instruments sold, not yet purchased	(2.0)	(1.5)
Note payable	(1.2)	(3.4)
Total debt	$ (1,387.6)	$ (1,186.0)