Investment Securities (Fair Value of Hedge Funds Subject to Restrictions on Redemption Frequency) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Hedge funds
Investment securities
Other long-term investments	$ 124.3
Private equity funds
Investment securities
Other long-term investments	129.8
Hedge and private equity funds included in other long-term investments
Investment securities
Other long-term investments	254.1	254.2
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	108.5	81.5
Private equity funds | Private Equity Multi Sector [Member]
Investment securities
Other long-term investments	29.3	26.9
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	6.4	8.2
Private equity funds | Private Equity Energy Infrastructure and Services [Member]
Investment securities
Other long-term investments	32.9	28.0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	11.7	9.9
Private equity funds | Private Equity Distressed Residential Real Estate [Member]
Investment securities
Other long-term investments	19.2	27.4
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0	0
Private equity funds | Real Estate Funds [Member]
Investment securities
Other long-term investments	12.2	9.5
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	3.3	3.3
Private equity funds | Private Equity Secondaries [Member]
Investment securities
Other long-term investments	11.0	11.3
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	3.2	4.0
Private equity funds | Private Equity Funds Multi Sector Europe [Member]
Investment securities
Other long-term investments	4.3	7.8
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	4.9	4.7
Private equity funds | Private Equity Funds Manufacturing and Industrial [Member]
Investment securities
Other long-term investments	10.6	6.2
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	29.1	0
Private equity funds | Private Equity Healthcare [Member]
Investment securities
Other long-term investments	4.3	2.3
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	5.4	7.0
Private equity funds | Private Equity Funds Multi Sector Asia [Member]
Investment securities
Other long-term investments	0.4	3.6
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	2.7	2.6
Private equity funds | Private Equity Insurance [Member]
Investment securities
Other long-term investments	3.2	3.5
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	41.3	41.3
Private equity funds | Venture Capital Funds [Member]
Investment securities
Other long-term investments	2.4	2.4
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0.5	0.5
Private equity funds | Private equity funds
Investment securities
Other long-term investments	129.8	128.9
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	108.5	81.5
Hedge funds | Hedge Funds, Equity [Member]
Investment securities
Other long-term investments	58.6	48.8
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0	0
Hedge funds | Hedge Funds Credit and Distressed [Member]
Investment securities
Other long-term investments	33.8	32.3
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0	0
Hedge funds | Hedge Funds Diversified Strategies [Member]
Investment securities
Other long-term investments	2.3	16.9
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0	0
Hedge funds | Hedge Funds Equity R E I T [Member]
Investment securities
Other long-term investments	15.2	14.5
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0	0
Hedge funds | Hedge Funds Equity Activist [Member]
Investment securities
Other long-term investments	14.0	12.3
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0	0
Hedge funds | Hedge Funds Bank Loan [Member]
Investment securities
Other long-term investments	0.4	0.5
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0	0
Hedge funds | Hedge funds
Investment securities
Other long-term investments	124.3	125.3
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0	$ 0