Investment Securities (Fair Value of Hedge Funds Subject to Restrictions on Redemption Frequency) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012	Dec. 31, 2011
Hedge funds
Investment securities
Other long-term investments	$ 117.2
Private equity funds
Investment securities
Other long-term investments	133.0
Hedge and private equity funds included in other long-term investments
Investment securities
Other long-term investments	250.2	[1]	239.8	[1]
Carrying value excluded associated with hedge funds and private equity funds	115.0	[1]	133.4	[1]
Private equity funds | Private Equity Secondaries
Investment securities
Other long-term investments	9.6		10.5
Carrying value excluded associated with hedge funds and private equity funds	3.1		3.1
Private equity funds | Private Equity Funds Multi Sector Europe
Investment securities
Other long-term investments	4.3		5.1
Carrying value excluded associated with hedge funds and private equity funds	4.9		5.0
Private equity funds | Private Equity Funds Manufacturing and Industrial
Investment securities
Other long-term investments	12.7		9.9
Carrying value excluded associated with hedge funds and private equity funds	15.5		29.1
Private equity funds | Private Equity Healthcare
Investment securities
Other long-term investments	7.0		4.3
Carrying value excluded associated with hedge funds and private equity funds	2.8		5.4
Private equity funds | Private Equity Funds Multi Sector Asia
Investment securities
Other long-term investments	0		0.4
Carrying value excluded associated with hedge funds and private equity funds	2.7		2.7
Private equity funds | Private Equity Insurance
Investment securities
Other long-term investments	2.4		3.0
Carrying value excluded associated with hedge funds and private equity funds	41.3		41.3
Private equity funds | Aerospace Defense Government
Investment securities
Other long-term investments	4.5		2.8
Carrying value excluded associated with hedge funds and private equity funds	20.5		22.2
Private equity funds | Venture Capital Funds
Investment securities
Other long-term investments	1.6		2.2
Carrying value excluded associated with hedge funds and private equity funds	0.3		0.3
Private equity funds | Private equity funds
Investment securities
Other long-term investments	133.0		125.2
Carrying value excluded associated with hedge funds and private equity funds	115.0		133.4
Level 3 Inputs | Fair value measured on a recurring basis | Other long-term investments
Investment securities
Carrying value of investment accounted for using the equity method	26.9		35.0		33.0	34.0
Private equity funds | Private Equity Multi Sector
Investment securities
Other long-term investments	26.6		23.3
Carrying value excluded associated with hedge funds and private equity funds	7.2		5.4
Private equity funds | Private Equity Energy Infrastructure and Services
Investment securities
Other long-term investments	45.5		36.3
Carrying value excluded associated with hedge funds and private equity funds	13.4		15.6
Private equity funds | Private Equity Distressed Residential Real Estate
Investment securities
Other long-term investments	9.4		15.8
Carrying value excluded associated with hedge funds and private equity funds	0		0
Private equity funds | Real Estate Funds
Investment securities
Other long-term investments	9.4		11.6
Carrying value excluded associated with hedge funds and private equity funds	3.3		3.3
Hedge funds | Hedge Funds, Equity
Investment securities
Other long-term investments	61.4		60.3
Carrying value excluded associated with hedge funds and private equity funds	0		0
Hedge funds | Hedge Funds Credit and Distressed
Investment securities
Other long-term investments	22.0		22.7
Carrying value excluded associated with hedge funds and private equity funds	0		0
Hedge funds | Hedge Funds Diversified Strategies
Investment securities
Other long-term investments	1.6		1.7
Carrying value excluded associated with hedge funds and private equity funds	0		0
Hedge funds | Hedge Funds Equity R E I T
Investment securities
Other long-term investments	16.7		16.0
Carrying value excluded associated with hedge funds and private equity funds	0		0
Hedge funds | Hedge Funds Equity Activist
Investment securities
Other long-term investments	15.3		13.6
Carrying value excluded associated with hedge funds and private equity funds	0		0
Hedge funds | Hedge Funds Bank Loan
Investment securities
Other long-term investments	0.2		0.3
Carrying value excluded associated with hedge funds and private equity funds	0		0
Hedge funds | Hedge funds
Investment securities
Other long-term investments	117.2		114.6
Carrying value excluded associated with hedge funds and private equity funds	$ 0		$ 0

[1] Excludes carrying value of $26.9 and $35.0 at September 30, 2013 and December 31, 2012 associated with hedge funds and private equity funds accounted for using the equity method.