Investment Securities (Fair Value of Hedge Funds Subject to Restrictions on Redemption Frequency) (Details) $ in Millions	Dec. 31, 2015 USD ($) fund	Dec. 31, 2014 USD ($)
Private equity funds
Investment securities
Number of Investments Held | fund	22
Trading Securities, Other	$ 90.8
Hedge funds
Investment securities
Number of Investments Held | fund	5
Trading Securities, Other	$ 37.0
Total hedge and private equity funds included in other long-term investments
Investment securities
Trading Securities, Other	127.8	$ 178.5
Fair value unfunded commitments	82.2	64.3
Other Long-term Investments Largest Single Investment	22.7	22.0
Private equity funds | Private equity funds
Investment securities
Trading Securities, Other	90.8	104.1
Fair value unfunded commitments	82.2	64.3
Private equity funds | Multi-sector
Investment securities
Trading Securities, Other	14.8	14.5
Fair value unfunded commitments	2.1	2.2
Private equity funds | Energy infrastructure & services
Investment securities
Trading Securities, Other	20.7	33.1
Fair value unfunded commitments	3.4	4.8
Private equity funds | Real estate
Investment securities
Trading Securities, Other	0.4	1.7
Fair value unfunded commitments	0.1	0.1
Private equity funds | Private equity secondaries
Investment securities
Trading Securities, Other	4.4	5.7
Fair value unfunded commitments	2.1	2.1
Private equity funds | Manufacturing/Industrial
Investment securities
Trading Securities, Other	24.9	23.2
Fair value unfunded commitments	2.5	7.3
Private equity funds | Healthcare
Investment securities
Trading Securities, Other	3.8	3.1
Fair value unfunded commitments	0.4	1.4
Private equity funds | Insurance
Investment securities
Trading Securities, Other	2.0	2.1
Fair value unfunded commitments	41.3	41.3
Private equity funds | Aerospace/Defense/Government
Investment securities
Trading Securities, Other	19.8	20.7
Fair value unfunded commitments	30.3	5.1
Hedge funds | Hedge funds
Investment securities
Trading Securities, Other	37.0	74.4
Fair value unfunded commitments	0.0	0.0
Hedge funds | Long/short credit & distressed
Investment securities
Trading Securities, Other	0.0	8.4
Fair value unfunded commitments	0.0	0.0
Hedge funds | Long/short equity REIT
Investment securities
Trading Securities, Other	20.6	20.4
Fair value unfunded commitments	0.0	0.0
Hedge funds | Other hedge funds
Investment securities
Trading Securities, Other	3.6	15.7
Fair value unfunded commitments	0.0	0.0
Hedge funds | Hedge Fund, Long/ Short Equity Banks and Financial [Member]
Investment securities
Trading Securities, Other	12.8	29.9
Fair value unfunded commitments	$ 0.0	$ 0.0