Basis of Presentation and Significant Accounting Policies (Policies)	6 Months Ended
Jun. 30, 2020
Basis of Presentation and Significant Accounting Policies
Basis of Presentation	Basis of Presentation In the opinion of management of Janus Henderson Group plc (“JHG,” “the Group,” “we,” “us,” “our” and similar terms), the accompanying unaudited condensed consolidated financial statements contain all normal recurring adjustments necessary to fairly state our financial position, results of operations and cash flows in accordance with accounting principles generally accepted in the United States of America (“GAAP”). Such financial statements have been prepared in accordance with the instructions to Form 10-Q pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These financial statements should be read in conjunction with the annual consolidated financial statements and notes presented in our Annual Report on Form 10-K for the year ended December 31, 2019. The December 31, 2019, condensed balance sheet data was derived from our audited financial statements, but does not include all disclosures required by GAAP. Events subsequent to the balance sheet date have been evaluated for inclusion in the accompanying financial statements through the issuance date.
Recent Accounting Pronouncements Adopted	Recent Accounting Pronouncements Adopted Implementation Costs — Cloud Computing Arrangements In August 2018, the Financial Accounting Standards Board (“FASB”) issued an accounting standards update (“ASU”) that aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement with the requirements for implementation costs incurred to develop or obtain internal-use software. The ASU is effective January 1, 2020, for calendar year-end companies and for the interim periods within those years. The ASU allows either a retrospective or prospective approach to all implementation costs incurred after adoption. We adopted the ASU effective January 1, 2020, using the prospective approach. There were no capitalized implementation costs incurred during the six-month period ended June 30, 2020. We generally expect increased capitalized costs as our previous policy dictated that implementation costs incurred in a hosting arrangement be expensed as incurred.
Recent Accounting Pronouncements Not Yet Adopted	Recent Accounting Pronouncements Not Yet Adopted Retirement Benefit Plans In August 2018, the FASB issued an ASU that modifies the disclosure requirements for employers that sponsor defined benefit pension plans. The ASU removes, adds and clarifies a number of disclosure requirements related to sponsored benefit plans. The standard is effective January 1, 2021, for calendar year-end companies, and early adoption is permitted. We are evaluating the effect of adopting this new accounting standard.

Basis of Presentation and Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2020

Basis of Presentation and Significant Accounting Policies

In the opinion of management of Janus Henderson Group plc (“JHG,” “the Group,” “we,” “us,” “our” and similar terms), the accompanying unaudited condensed consolidated financial statements contain all normal recurring adjustments necessary to fairly state our financial position, results of operations and cash flows in accordance with accounting principles generally accepted in the United States of America (“GAAP”). Such financial statements have been prepared in accordance with the instructions to Form 10-Q pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These financial statements should be read in conjunction with the annual consolidated financial statements and notes presented in our Annual Report on Form 10-K for the year ended December 31, 2019. The December 31, 2019, condensed balance sheet data was derived from our audited financial statements, but does not include all disclosures required by GAAP. Events subsequent to the balance sheet date have been evaluated for inclusion in the accompanying financial statements through the issuance date.

Recent Accounting Pronouncements Adopted

Implementation Costs — Cloud Computing Arrangements

In August 2018, the Financial Accounting Standards Board (“FASB”) issued an accounting standards update (“ASU”) that aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement with the requirements for implementation costs incurred to develop or obtain internal-use software. The ASU is effective January 1, 2020, for calendar year-end companies and for the interim periods within those years. The ASU allows either a retrospective or prospective approach to all implementation costs incurred after adoption. We adopted the ASU effective January 1, 2020, using the prospective approach. There were no capitalized implementation costs incurred during the six-month period ended June 30, 2020. We generally expect increased capitalized costs as our previous policy dictated that implementation costs incurred in a hosting arrangement be expensed as incurred.

Recent Accounting Pronouncements Not Yet Adopted

Retirement Benefit Plans

In August 2018, the FASB issued an ASU that modifies the disclosure requirements for employers that sponsor defined benefit pension plans. The ASU removes, adds and clarifies a number of disclosure requirements related to sponsored benefit plans. The standard is effective January 1, 2021, for calendar year-end companies, and early adoption is permitted. We are evaluating the effect of adopting this new accounting standard.