Investment Securities (Fair Value of Hedge Funds Subject to Restrictions on Redemption Frequency) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Hedge funds
Investment securities
Other long-term investments	$ 126.2
Private equity funds
Investment securities
Other long-term investments	124.9
Hedge and private equity funds included in other long-term investments
Investment securities
Other long-term investments	251.1	239.0
Unfunded Commitments	106.1	110.6
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	25.0	26.6	34.9	35.0
Private equity funds | Private Equity Multi Sector
Investment securities
Other long-term investments	24.1	23.8
Unfunded Commitments	6.4	6.5
Private equity funds | Private Equity Energy Infrastructure and Services
Investment securities
Other long-term investments	46.8	45.9
Unfunded Commitments	12.7	13.1
Private equity funds | Real Estate Funds
Investment securities
Other long-term investments	7.1	8.2
Unfunded Commitments	3.3	3.3
Private equity funds | Private Equity Secondaries
Investment securities
Other long-term investments	9.2	9.5
Unfunded Commitments	3.1	3.1
Private equity funds | Private Equity Funds Multi Sector Europe
Investment securities
Other long-term investments	3.8	3.9
Unfunded Commitments	2.8	2.8
Private equity funds | Private Equity Funds Manufacturing and Industrial
Investment securities
Other long-term investments	11.5	11.2
Unfunded Commitments	15.2	15.5
Private equity funds | Private Equity Healthcare
Investment securities
Other long-term investments	7.8	5.6
Unfunded Commitments	2.8	2.8
Private equity funds | Private Equity Funds Multi Sector Asia
Investment securities
Other long-term investments	0	0
Unfunded Commitments	2.7	2.7
Private equity funds | Private Equity Insurance
Investment securities
Other long-term investments	2.4	2.3
Unfunded Commitments	41.3	41.3
Private equity funds | Aerospace Defense Government
Investment securities
Other long-term investments	10.6	5.8
Unfunded Commitments	15.5	19.2
Private equity funds | Venture Capital Funds
Investment securities
Other long-term investments	1.6	1.6
Unfunded Commitments	0.3	0.3
Private equity funds | Private equity funds
Investment securities
Other long-term investments	124.9	118.2
Unfunded Commitments	106.1	110.6
Hedge funds | Hedge Funds, Equity Long (Short) [Member]
Investment securities
Other long-term investments	67.6	62.6
Unfunded Commitments	0	0
Hedge funds | Hedge Funds Credit and Distressed
Investment securities
Other long-term investments	23.3	22.8
Unfunded Commitments	0	0
Hedge funds | Hedge Funds Diversified Strategies
Investment securities
Other long-term investments	0	0.1
Unfunded Commitments	0	0
Hedge funds | Hedge Funds Equity R E I T
Investment securities
Other long-term investments	18.8	18.3
Unfunded Commitments	0	0
Hedge funds | Hedge Funds Equity Activist
Investment securities
Other long-term investments	16.3	16.8
Unfunded Commitments	0	0
Hedge funds | Hedge Funds Bank Loan
Investment securities
Other long-term investments	0.2	0.2
Unfunded Commitments	0	0
Hedge funds | Hedge funds
Investment securities
Other long-term investments	126.2	120.8
Unfunded Commitments	$ 0	$ 0