Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Total revenue	$ 516.5	$ 555.5	$ 1,012.3	$ 1,175.5
Operating expenses:
Employee compensation and benefits	147.7	145.0	288.0	309.6
Long-term incentive plans	37.6	40.7	93.1	92.1
Distribution expenses	114.6	127.8	226.6	269.6
Investment administration	11.1	10.3	22.7	25.1
Marketing	9.3	7.8	18.1	15.2
General, administrative and occupancy	72.2	72.3	133.3	145.4
Depreciation and amortization	6.1	7.7	12.2	17.2
Total operating expenses	398.6	411.6	794.0	874.2
Operating income:	117.9	143.9	218.3	301.3
Interest expense	(3.2)	(3.2)	(6.3)	(6.4)
Investment gains (losses), net	6.9	(109.4)	24.5	(141.6)
Other non-operating income (expenses), net	7.0	0.6	14.1	(7.2)
Income before taxes	128.6	31.9	250.6	146.1
Income tax benefit (provision)	(28.2)	(36.7)	(54.2)	(67.4)
Net income (loss)	100.4	(4.8)	196.4	78.7
Net loss (income) attributable to noncontrolling interests	(10.6)	101.0	(19.2)	121.1
Net income attributable to JHG	$ 89.8	$ 96.2	$ 177.2	$ 199.8
Earnings (loss) per share attributable to JHG common shareholders:
Basic (in dollars per share)	$ 0.54	$ 0.58	$ 1.07	$ 1.19
Diluted (in dollars per share)	$ 0.54	$ 0.57	$ 1.07	$ 1.19
Other comprehensive income (loss), net of tax:
Foreign currency translation gains (losses)	$ 40.5	$ (177.8)	$ 85.0	$ (224.8)
Actuarial gains	0.1	0.1	0.2	0.2
Other comprehensive income (loss), net of tax	40.6	(177.7)	85.2	(224.6)
Other comprehensive loss (income) attributable to noncontrolling interests	1.6	23.6	(1.6)	23.4
Other comprehensive income (loss) attributable to JHG	42.2	(154.1)	83.6	(201.2)
Total comprehensive income (loss)	141.0	(182.5)	281.6	(145.9)
Total comprehensive loss (income) attributable to noncontrolling interests	(9.0)	124.6	(20.8)	144.5
Total comprehensive income (loss) attributable to JHG	132.0	(57.9)	260.8	(1.4)
Investment Advice [Member]
Total revenue	423.5	453.6	838.1	967.6
Investment Performance [Member]
Total revenue	(5.9)	(3.4)	(20.8)	(11.8)
Shareholder Service [Member]
Total revenue	53.3	56.3	104.8	118.7
Product and Service, Other [Member]
Total revenue	$ 45.6	$ 49.0	$ 90.2	$ 101.0