Variable Interest Entities - Unconsolidated VIEs (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Sponsored Investment Funds
Total assets of unconsolidated money market mutual fund variable interest entities	$ 1,300.0	$ 1,400.0
Other investments: Other limited partnership and fund interests
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	255.6	188.2
Maximum exposure to loss	255.6	188.2
Available-for-sale \| Corporate debt securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	453.4	456.7
Maximum exposure to loss	359.8	353.3
Available-for-sale \| Residential mortgage-backed pass-through securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	2,627.5	2,822.9
Maximum exposure to loss	2,549.4	2,702.9
Available-for-sale \| Commercial mortgage-backed securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	3,919.8	3,975.5
Maximum exposure to loss	3,932.5	3,896.9
Available-for-sale \| Collateralized debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	667.5	504.1
Maximum exposure to loss	692.7	521.2
Available-for-sale \| Other debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	4,530.8	4,616.4
Maximum exposure to loss	4,527.3	4,583.4
Trading \| Residential mortgage-backed pass-through securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	25.9	34.4
Maximum exposure to loss	25.9	34.4
Trading \| Commercial mortgage-backed securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	2.3	1.5
Maximum exposure to loss	2.3	1.5
Trading \| Collateralized debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	35.1	39.4
Maximum exposure to loss	$ 35.1	39.4
Trading \| Other debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value		0.2
Maximum exposure to loss		$ 0.2

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- Definition

Total assets held by money market mutual funds that are deemed to be variable interest entities but are not consolidated by the entity, as it is not the primary beneficiary.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph b
-URI http://asc.fasb.org/extlink&oid=52262685&loc=d3e5728-111685

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=52262685&loc=d3e5747-111685

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- Definition

Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

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