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Investment Securities (Fair Value of Hedge Funds Subject to Restrictions on Redemption Frequency) (Details) $ in Millions	Dec. 31, 2016 USD ($) fund	Dec. 31, 2015 USD ($)
Private equity funds
Investment securities
Number of Investments Held | fund	23
Trading Securities, Other	$ 71.2
Hedge funds
Investment securities
Number of Investments Held | fund	5
Trading Securities, Other	$ 59.8
Total hedge and private equity funds included in other long-term investments
Investment securities
Trading Securities, Other	131.0	$ 127.8
Fair value unfunded commitments	138.1	82.2
Other Long-term Investments Largest Single Investment	36.5	22.7
Private equity funds | Private equity funds
Investment securities
Trading Securities, Other	71.2	90.8
Fair value unfunded commitments	138.1	82.2
Private equity funds | Multi-sector
Investment securities
Trading Securities, Other	11.4	14.8
Fair value unfunded commitments	2.0	2.1
Private equity funds | Energy infrastructure & services
Investment securities
Trading Securities, Other	14.1	20.7
Fair value unfunded commitments	3.2	3.4
Private equity funds | Real estate
Investment securities
Trading Securities, Other	0.3	0.4
Fair value unfunded commitments	0.1	0.1
Private equity funds | Private equity secondaries
Investment securities
Trading Securities, Other	3.0	4.4
Fair value unfunded commitments	2.1	2.1
Private equity funds | Direct Lending [Member]
Investment securities
Trading Securities, Other	1.8
Fair value unfunded commitments	35.7
Private equity funds | Financial Services Sector
Investment securities
Trading Securities, Other	1.0
Fair value unfunded commitments	5.0
Private equity funds | Healthcare
Investment securities
Trading Securities, Other	3.5	3.8
Fair value unfunded commitments	0.4	0.4
Private equity funds | Insurance
Investment securities
Trading Securities, Other	0.8	2.0
Fair value unfunded commitments	41.3	41.3
Private equity funds | Aerospace/Defense/Government
Investment securities
Trading Securities, Other	19.4	19.8
Fair value unfunded commitments	25.9	30.3
Private equity funds | Industrial
Investment securities
Trading Securities, Other	15.9	24.9
Fair value unfunded commitments	22.4	2.5
Hedge funds | Hedge Fund, Long/ Short Equity Banks and Financial [Member]
Investment securities
Trading Securities, Other	36.5	12.8
Fair value unfunded commitments	0.0	0.0
Hedge funds | Hedge funds
Investment securities
Trading Securities, Other	59.8	37.0
Fair value unfunded commitments	0.0	0.0
Hedge funds | Long/short equity REIT
Investment securities
Trading Securities, Other	19.9	20.6
Fair value unfunded commitments	0.0	0.0
Hedge funds | Other hedge funds
Investment securities
Trading Securities, Other	3.4	3.6
Fair value unfunded commitments	$ 0.0	$ 0.0

X

- Definition

The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Trading Securities
-URI http://asc.fasb.org/extlink&oid=6526789

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26626-111562

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.(a),1(c),(d),(e),(f),(g))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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