Accounting Policies (Policy)	3 Months Ended
Accounting Policies (Policy)	Mar. 31, 2017
Accounting Policies [Abstract]
Basis of Accounting and Consolidation	Basis of Accounting and Consolidation The unaudited Condensed Consolidated Financial Statements have been prepared in accordance with accounting principles generally accepted in the United States for interim financial information and with rules and regulations of the Securities and Exchange Commission and consolidate the financial statements of the Parent and all of its controlled subsidiaries. In the opinion of management, the financial statements reflect all adjustments, consisting of normal recurring accruals, which are necessary for the fair statement of the financial condition and results of operations for the periods presented. All significant intercompany transactions, balances, revenues and expenses are eliminated upon consolidation.
Management and Investment Advisory Fees, Policy [Policy Text Block]	Money Market Fee Waivers The company is currently voluntarily providing yield support waivers of its management fees on certain money market funds to ensure that they maintain a minimum level of daily net investment income. During the three months ended March 31, 2017, yield support waivers resulted in a reduction of management and service and distribution fees of approximately $1.7 million. During the three months ended March 31, 2017, approximately 62% of yield support waivers are offset by a reduction in third party distribution, service and advisory expenses, resulting in a net waiver of $0.6 million. The company has provided yield support waivers in prior periods and may increase or decrease the level of fee waivers in future periods.
Accounting Pronouncements Recently Adopted and Pending Accounting Pronouncements	Accounting Pronouncements Recently Adopted and Pending Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update 2014-09, “Revenue from Contracts with Customers” (ASU 2014-09) which revises revenue recognition criteria and expands disclosure requirements. This new guidance will be effective for interim and annual reporting periods beginning after December 15, 2017. Early adoption is permitted but only for interim and annual reporting periods beginning after December 15, 2016. The company has elected to implement this new accounting standard on January 1, 2018. However, a decision on the adoption method has not been made as of the date of this Report. There are certain elements of this new accounting guidance that are still being interpreted. During 2015 and 2016, the Financial Accounting Standards Board (FASB) issued several updates to various aspects of the guidance relevant to the company’s implementation assessment, including clarifications on principal versus agent considerations, the identification and disclosure of performance obligations, and other narrow-scope amendments. The underlying premise of the new guidance requires the employment of a five step model to determine the amount of revenue that reflects the consideration to which the company expects to be entitled for the transfer of services to customers and the timing of recognition. In addition, ASU 2014-09 also requires certain costs to obtain and fulfill contracts with customers to be capitalized, if they meet certain criteria. Capitalized contract costs are subject to amortization and periodic impairment testing. A key part of management’s implementation efforts is the detailed review of the terms and conditions of a sample of revenue contracts covering a broad range of products across geographic locations. This assessment is largely complete. The company does not anticipate a significant change in the timing of revenue recognition for management and service fee revenues. Performance fees (including carried interest) are under evaluation; the timing of recognition will be driven by the terms of each performance fee arrangement. We continue to assess the impact of the rule changes on required disclosures, the accounting for costs associated with revenue contracts, and gross versus net revenue presentation. The above findings are based on our work performed to date. Further impacts may be identified as we continue our assessment and as additional guidance (including interpretive guidance) is issued. In March 2016, the FASB issued Accounting Standards Update 2016-09, “Compensation - Stock Compensation: Improvements to Employee Share-Based Payment Accounting” (ASU 2016-09). The standard is intended to simplify aspects of the accounting for share-based payment transactions, including income tax impacts, classification on the statement of cash flows, and forfeitures. The company adopted ASU 2016-09 on January 1, 2017. One of the impacts of the new rules is that excess tax benefits and tax deficiencies related to vested awards are no longer recorded in additional paid-in-capital but rather as an income tax expense or benefit. This provision requires a prospective approach to adoption. In the three months ended March 31, 2017, the recognition of excess tax benefits reduced our income tax provision by $1.3 million. Another change resulting from the adoption of ASU 2016-09 relates to the presentation of excess tax benefits and tax deficiencies in the Condensed Consolidated Statement of Cash Flows. The standard requires that excess tax benefits and tax deficiencies be shown as operating cash flows within the Condensed Consolidated Statement of Cash Flows; previously, the company reported these cash flow activities as financing cash flows. The company elected to use a prospective approach to adoption related to this provision and in the three months ended March 31, 2017, $1.3 million cash inflows were included within the increase/(decrease) in payables as an operating cash flow in the Condensed Consolidated Statement of Cash Flows. ASU 2016-09 requires that employee taxes paid when shares are withheld for tax withholding purposes be reported as a financing activity in the Condensed Consolidated Statement of Cash Flows. The company has retrospectively adopted this change and included $52.5 million in financing activities for the three months ended March 31, 2017 (three months ended March 31, 2016: $36.6 million). Additionally, the new rules allow companies to elect to continue to account for forfeitures using an estimate or instead to elect to account for forfeitures as they occur. The company elected to continue to account for forfeitures using an estimate. The company anticipates fluctuations in its effective tax rate as a result of the excess tax benefits or tax deficiencies being recorded to the income tax provision, particularly in the first quarter of each year when annual share awards vest. In October 2016, the FASB issued Accounting Standards Update 2016-17, “Consolidation: Interests Held through Related Parties That Are under Common Control” (ASU 2016-17). The standard addresses how a reporting entity determines if it satisfies the characteristics of a primary beneficiary of a variable interest entity (VIE) and which party within a group is considered the primary beneficiary. The company adopted ASU 2016-17 on January 1, 2017 and determined that this guidance did not materially change the company's consolidation conclusions. In February 2017, the FASB issued Accounting Standards Update 2017-05, “Other Income-Gains and Losses from the Derecognition of Nonfinancial Assets: Clarifying the Scope of Asset Derecognition Guidance and Accounting for Partial Sales of Nonfinancial Assets” (ASU 2017-05). The standard clarifies the scope of accounting for gains and losses from the derecognition of nonfinancial assets and adds guidance for partial sales of nonfinancial assets. ASU 2017-05 is effective for fiscal years and interim periods within those years beginning after December 15, 2017 and must be adopted at the same time as ASU 2014-09. The amendments allow either a retrospective or modified retrospective approach to adoption, and early adoption is permitted. The company is currently evaluating the impact of this standard. In March 2017, the FASB issued Accounting Standard Update 2017-07, “Compensation-Retirement Benefits: Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost” (ASU 2017-07). The amendments require that an employer disaggregate the service cost component from the other components of net benefit cost. The amendments also provide guidance on how to present the service cost component and the other components of net benefit cost in the income statement and allow that only the service cost component of net benefit cost is eligible for capitalization. ASU 2017-07 is effective for fiscal years and interim periods within those years beginning after December 15, 2017, and early adoption is permitted as of the beginning of an annual period for which financial statements have not been issued or made available of issuance. The amendments require primarily a retrospective approach to adoption. The company is currently evaluating the impact of this standard.
Fair Value Measurement	The following is a description of the valuation methodologies used for assets and liabilities measured at fair value, as well as the general classification of such assets and liabilities pursuant to the valuation hierarchy. Cash equivalents Cash investments in money market funds are valued under the market approach through the use of quoted market prices in an active market, which is the net asset value of the underlying funds, and are classified within level 1 of the valuation hierarchy. Available-for-sale investments Seed money is valued under the market approach through the use of quoted market prices available in an active market and is classified within level 1 of the valuation hierarchy; there is no modeling or additional information needed to arrive at the fair values of these investments. At March 31, 2017 and December 31, 2016, investments in collateralized loan obligations (CLOs) were valued using pricing information obtained by an independent third-party pricing source. Other debt securities are valued using a cost valuation technique due to the lack of available cash flow and market data and are accordingly classified within level 3 of the valuation hierarchy. Trading investments •Investments related to deferred compensation plans Investments related to deferred compensation plans are valued under the market approach through the use of quoted prices in an active market and are classified within level 1 of the valuation hierarchy. •Seed money Seed money is valued under the market approach through the use of quoted market prices available in an active market and is classified within level 1 of the valuation hierarchy; there is no modeling or additional information needed to arrive at the fair values of these investments. •Other equity securities Other equity securities consist of investments in publicly-traded equity securities. These securities are valued under the market approach through the use of quoted prices on an exchange. To the extent these securities are actively traded, valuation adjustments are not applied and they are categorized within level 1 of the valuation hierarchy; otherwise, they are categorized in level 2. •UIT-related equity and debt securities The company invests in Unit Investment Trust (UIT)-related equity and debt securities consisting of investments in corporate equities, UITs, and municipal securities. Each is discussed more fully below. Corporate equities The company temporarily holds investments in corporate equities for purposes of creating a UIT. Corporate equities are valued under the market approach through use of quoted prices on an exchange. To the extent these securities are actively traded, valuation adjustments are not applied and they are categorized within level 1 of the valuation hierarchy; otherwise, they are categorized in level 2. UITs The company may hold units of its sponsored UITs at period-end for sale in the primary market or secondary market. Equity UITs are valued under the market approach through use of quoted prices on an exchange. Fixed income UITs are valued using recently executed transaction prices, market price quotations (where observable), bond spreads, or credit default swap spreads. The spread data used is for the same maturities as the underlying bonds. If the spread data does not reference the issuers, then data that references comparable issuers is used. When observable price quotations are not available, fair value is determined based on cash flow models with yield curves, bond or single name credit default spreads, and recovery rates based on collateral value as key inputs. Depending on the nature of the inputs, these investments are categorized as level 1, 2, or 3. Put option contracts The company has purchased put option contracts to hedge economically foreign currency risk on the translation of a portion of its Pound Sterling-denominated earnings and Euro-denominated earnings into U.S. Dollars (purchases of $4.2 million and $7.0 million in the three months ended March 31, 2017 and March 31, 2016, respectively). These were the only contracts entered into during the period to hedge economically foreign currency risk on the translation of a portion of the Pound Sterling-denominated earnings and provide coverage through June 29, 2018. The contracts entered into during 2016 to hedge economically foreign currency risk on the translation of a portion of the Euro-denominated earnings provide coverage through December 27, 2017. The economic hedge is predominantly triggered upon the impact of a significant decline in the respective Pound Sterling/U.S. Dollar foreign exchange rate or Euro/U.S. Dollar foreign exchange rate. Open put option contracts are marked-to-market through earnings, which are recorded in the company's Condensed Consolidated Statements of Income in other gains and losses, net. These derivative contracts are valued using option valuation models and are included in other assets in the company's Condensed Consolidated Balance Sheets. The significant inputs in these models (volatility, forward points and swap curves) are readily available in public markets or can be derived from observable market transactions for substantially the full terms of the contracts and are classified within level 2 of the valuation hierarchy. The company recognized a $8.2 million net loss in the three months ended March 31, 2017 (three months ended March 31, 2016: $2.5 million net gain) related to the change in market value of these put option contracts. Assets held for policyholders Assets held for policyholders are measured at fair value under the market approach based on the quoted prices of the underlying funds in an active market and are classified within level 1 of the valuation hierarchy. The policyholder payables are indexed to the value of the assets held for policyholders and are therefore not included in the tables below. Contingent Consideration Liability During 2015, the company acquired certain investment management contracts from Deutsche Bank. Indefinite-lived intangible assets were valued at $119.3 million. This transaction was a non-cash investing activity during that period. The purchase price was comprised solely of contingent consideration payable in future periods, and is linked to future revenues generated from the contracts. The contingent consideration liability was recorded at fair value as of the date of acquisition using a discounted cash flow model, and is categorized within level 3 of the valuation hierarchy. Anticipated future cash flows were determined using forecasted assets under management (AUM) levels and discounted back to the valuation date. The company reassesses significant unobservable inputs during each reporting period. At March 31, 2017 inputs used in the model included assumed growth rates in AUM ranging from 0.69% to 4.4% (weighted average growth rate of 2.48%) and a discount rate of 3.88%. Changes in fair value are recorded in other gains and losses, net in the Condensed Consolidated Statements of Income in the period incurred. An increase in AUM levels and a decrease in the discount rate would increase the fair value of the contingent consideration liability while a decrease in forecasted AUM and an increase in the discount rate would decrease the liability.