CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue:
Total revenue	$ 2,298.6	$ 2,192.4	$ 2,306.4
Operating expenses:
Employee compensation and benefits	618.6	602.5	613.0
Long-term incentive plans	170.1	184.3	188.6
Distribution expenses	464.4	444.3	446.7
Investment administration	50.0	47.9	46.9
Marketing	19.6	31.1	37.9
General, administrative and occupancy	255.2	260.8	253.7
Impairment of goodwill and intangible assets	513.7	18.0	7.2
Depreciation and amortization	49.2	62.6	62.6
Total operating expenses	2,140.8	1,651.5	1,656.6
Operating income	157.8	540.9	649.8
Interest expense	(12.9)	(15.1)	(15.7)
Investment gains (losses), net	57.5	34.2	(40.9)
Other non-operating income, net	39.7	23.5	68.6
Income before taxes	242.1	583.5	661.8
Income tax provision	(59.5)	(137.8)	(162.2)
Net income	182.6	445.7	499.6
Net loss (income) attributable to noncontrolling interests	(21.0)	(18.1)	24.2
Net income attributable to JHG	$ 161.6	$ 427.6	$ 523.8
Earnings per share attributable to JHG common shareholders:
Basic (in dollars per share)	$ 0.87	$ 2.21	$ 2.62
Diluted (in dollars per share)	$ 0.87	$ 2.21	$ 2.61
Other comprehensive income (loss), net of tax:
Foreign currency translation gains (losses)	$ 71.8	$ 74.7	$ (124.3)
Actuarial gains (losses)	(29.5)	(5.6)	3.7
Other comprehensive income (loss), net of tax	42.3	69.1	(120.6)
Other comprehensive loss (income) attributable to noncontrolling interests	0.8	(12.7)	1.4
Other comprehensive income (loss) attributable to JHG	43.1	56.4	(119.2)
Total comprehensive income	224.9	514.8	379.0
Total comprehensive loss (income) attributable to noncontrolling interests	(20.2)	(30.8)	25.6
Total comprehensive income attributable to JHG	204.7	484.0	404.6
Management fees
Revenue:
Total revenue	1,794.1	1,792.3	1,947.4
Performance fees
Revenue:
Total revenue	98.1	17.6	7.1
Shareowner servicing fees
Revenue:
Total revenue	209.2	185.4	154.2
Other revenue
Revenue:
Total revenue	$ 197.2	$ 197.1	$ 197.7