Investment Securities (Fair Value of Hedge Funds Subject to Restrictions on Redemption Frequency) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Private equity funds
Investment securities
Number of Investments Held	32
Trading Securities, Other	$ 150.9
Hedge funds
Investment securities
Number of Investments Held	12
Trading Securities, Other	92.0
Total hedge and private equity funds included in other long-term investments
Investment securities
Trading Securities, Other	242.9	239.0
Fair value unfunded commitments	81.7	110.6
Other Long-term Investments Largest Single Investment	22.0	18.3
Private equity funds | Private equity funds
Investment securities
Trading Securities, Other	150.9	118.2
Fair value unfunded commitments	81.7	110.6
Private equity funds | Multi-sector
Investment securities
Trading Securities, Other	24.2	23.8
Fair value unfunded commitments	5.3	6.5
Private equity funds | Energy infrastructure & services
Investment securities
Trading Securities, Other	59.6	45.9
Fair value unfunded commitments	11.0	13.1
Private equity funds | Distressed residential real estate
Investment securities
Trading Securities, Other	0	0.4
Fair value unfunded commitments	0	0
Private equity funds | Real estate
Investment securities
Trading Securities, Other	3.6	8.2
Fair value unfunded commitments	3.3	3.3
Private equity funds | Private equity secondaries
Investment securities
Trading Securities, Other	8.5	9.5
Fair value unfunded commitments	3.1	3.1
Private equity funds | International multi-sector, Europe
Investment securities
Trading Securities, Other	1.5	3.9
Fair value unfunded commitments	2.3	2.8
Private equity funds | Manufacturing/Industrial
Investment securities
Trading Securities, Other	23.2	11.2
Fair value unfunded commitments	7.3	15.5
Private equity funds | Healthcare
Investment securities
Trading Securities, Other	6.1	5.6
Fair value unfunded commitments	2.8	2.8
Private equity funds | International multi-sector, Asia
Investment securities
Trading Securities, Other	0	0
Fair value unfunded commitments	0	2.7
Private equity funds | Insurance
Investment securities
Trading Securities, Other	2.1	2.3
Fair value unfunded commitments	41.2	41.3
Private equity funds | Aerospace/Defense/Government
Investment securities
Trading Securities, Other	20.7	5.8
Fair value unfunded commitments	5.1	19.2
Private equity funds | Venture capital
Investment securities
Trading Securities, Other	1.4	1.6
Fair value unfunded commitments	0.3	0.3
Hedge funds | Hedge funds
Investment securities
Trading Securities, Other	92.0	120.8
Fair value unfunded commitments	0	0
Hedge funds | Long/short equity
Investment securities
Trading Securities, Other	43.9	62.6
Fair value unfunded commitments	0	0
Hedge funds | Long/short credit & distressed
Investment securities
Trading Securities, Other	21.4	22.8
Fair value unfunded commitments	0	0
Hedge funds | Long diversified strategies
Investment securities
Trading Securities, Other	0	0.1
Fair value unfunded commitments	0	0
Hedge funds | Long/short equity REIT
Investment securities
Trading Securities, Other	20.3	18.3
Fair value unfunded commitments	0	0
Hedge funds | Long/short equity activist
Investment securities
Trading Securities, Other	6.2	16.8
Fair value unfunded commitments	0	0
Hedge funds | Long bank loan
Investment securities
Trading Securities, Other	0.2	0.2
Fair value unfunded commitments	0	0
DavidShield [Member]
Investment securities
Fair value unfunded commitments	$ 21.0