Variable Interest Entities (Details 2) - USD ($) $ in Millions	Jun. 30, 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	203.4	188.2
Maximum exposure to loss	203.4	188.2
Available-for-sale \| Corporate debt securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	447.6	456.7
Maximum exposure to loss	354.5	353.3
Available-for-sale \| Residential mortgage-backed pass-through securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	2,666.5	2,822.9
Maximum exposure to loss	2,573.3	2,702.9
Available-for-sale \| Commercial mortgage-backed securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	3,875.2	3,975.5
Maximum exposure to loss	3,810.5	3,896.9
Available-for-sale \| Collateralized debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	642.0	504.1
Maximum exposure to loss	660.1	521.2
Available-for-sale \| Other debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	4,525.1	4,616.4
Maximum exposure to loss	4,494.3	4,583.4
Trading \| Residential mortgage-backed pass-through securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	29.5	34.4
Maximum exposure to loss	29.5	34.4
Trading \| Commercial mortgage-backed securities
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	1.6	1.5
Maximum exposure to loss	1.6	1.5
Trading \| Collateralized debt obligations
Unconsolidated Variable Interest Entity disclosures
Asset carrying value	39.4	39.4
Maximum exposure to loss	$ 39.4	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.

+ References

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.

+ References

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