Business Segment Information - Schedule of Business Segment Information (Details) $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of business segments | segment									2
Segment Reporting Information, Additional Information [Abstract]
Net sales by product	$ 547.0	$ 491.7	$ 521.3	$ 508.3	$ 537.5	$ 485.0	$ 524.8	$ 503.6	$ 2,068.3	$ 2,050.9	$ 1,851.6
Income (loss) from operations									334.3	305.6	266.4
Non-operating expense:
Interest expense, net									(58.6)	(69.9)	(75.1)
Gain (loss) on the extinguishment of debt									1.0	4.3	(11.9)
Actuarial (loss) gain on pension and postretirement benefit obligations	(35.8)								(36.6)	0.4	3.3
Other (expense) income, net									(3.8)	(1.6)	4.4
Income from continuing operations before income taxes									236.3	238.8	187.1
(Provision) benefit for income taxes									(54.1)	(53.4)	19.5
Equity method investment income									0.0	3.6	0.0
Net income from continuing operations	28.6	48.4	56.7	48.5	47.7	52.9	46.2	42.2	182.2	189.0	206.6
Loss from discontinued operations, net of tax	0.0	0.0	0.0	(1.8)	(0.4)	(27.8)	(83.7)	(42.8)	(1.8)	(154.7)	(130.6)
Net income	28.6	48.4	56.7	46.7	47.3	25.1	(37.5)	(0.6)	180.4	34.3	76.0
Non-controlling interest income	0.1	(0.1)	0.1	0.2	0.1	(0.3)	0.1	0.1	0.3	0.0	0.1
Net income attributable to Rexnord	28.5	48.5	56.6	46.5	47.2	25.4	(37.6)	(0.7)	180.1	34.3	75.9
Dividends on preferred stock	0.0	(2.8)	(5.8)	(5.8)	(5.8)	(5.8)	(5.8)	(5.8)	(14.4)	(23.2)	(23.2)
Net income attributable to Rexnord common stockholders	28.5	$ 45.7	$ 50.8	$ 40.7	41.4	$ 19.6	$ (43.4)	$ (6.5)	165.7	11.1	52.7
Depreciation and Amortization									86.6	87.9	79.7
Capital Expenditures									41.4	42.5	38.0
Total Assets	3,627.1				3,259.7				3,627.1	3,259.7	3,423.7
Segments, Geographical Areas [Abstract]
Net Sales									2,068.3	2,050.9	1,851.6
Long-lived Assets	378.8				383.0				378.8	383.0	396.5
United States
Segments, Geographical Areas [Abstract]
Net Sales									1,472.7	1,460.6	1,361.6
Long-lived Assets	264.7				260.7				264.7	260.7	260.9
Europe
Segments, Geographical Areas [Abstract]
Net Sales									298.9	327.5	255.5
Long-lived Assets	72.9				78.9				72.9	78.9	91.2
Rest of World
Segments, Geographical Areas [Abstract]
Net Sales									296.7	262.8	234.5
Long-lived Assets	41.2				43.4				41.2	43.4	44.4
Process & Motion Control
Segment Reporting Information, Additional Information [Abstract]
Net sales by product									1,358.2	1,380.6	1,241.2
Process & Motion Control | Europe
Segment Reporting Information, Additional Information [Abstract]
Net sales by product									298.9	327.5	255.5
Water Management
Segment Reporting Information, Additional Information [Abstract]
Net sales by product									710.1	670.3	610.4
Water Management | Europe
Segment Reporting Information, Additional Information [Abstract]
Net sales by product									0.0	0.0	0.0
Operating Segments | Process & Motion Control
Segment Reporting Information, Additional Information [Abstract]
Income (loss) from operations									228.4	226.1	191.3
Non-operating expense:
Depreciation and Amortization									59.6	63.0	56.0
Capital Expenditures									34.6	36.3	34.2
Total Assets	2,953.0				2,677.7				2,953.0	2,677.7	2,598.8
Operating Segments | Water Management
Segment Reporting Information, Additional Information [Abstract]
Income (loss) from operations									163.1	139.7	125.7
Non-operating expense:
Depreciation and Amortization									26.5	24.9	23.7
Capital Expenditures									6.8	6.2	3.8
Total Assets	656.7				576.8				656.7	576.8	820.9
Corporate
Segment Reporting Information, Additional Information [Abstract]
Income (loss) from operations									(57.2)	(60.2)	(50.6)
Non-operating expense:
Depreciation and Amortization									0.5	0.0	0.0
Total Assets	$ 17.4				$ 5.2				17.4	5.2	4.0
Original equipment manufacturers/ end-users | Process & Motion Control
Segment Reporting Information, Additional Information [Abstract]
Net sales by product									766.8	768.5	690.5
Original equipment manufacturers/ end-users | Operating Segments | Process & Motion Control
Segment Reporting Information, Additional Information [Abstract]
Net sales by product									766.8	768.5	690.5
Maintenance, repair, and operations | Process & Motion Control
Segment Reporting Information, Additional Information [Abstract]
Net sales by product									591.4	612.1	550.7
Maintenance, repair, and operations | Operating Segments | Process & Motion Control
Segment Reporting Information, Additional Information [Abstract]
Net sales by product									591.4	612.1	550.7
Water safety, quality, flow control and conservation | Water Management
Segment Reporting Information, Additional Information [Abstract]
Net sales by product									661.0	624.4	566.9
Water safety, quality, flow control and conservation | Operating Segments | Water Management
Segment Reporting Information, Additional Information [Abstract]
Net sales by product									661.0	624.4	566.9
Water infrastructure | Water Management
Segment Reporting Information, Additional Information [Abstract]
Net sales by product									49.1	45.9	43.5
Water infrastructure | Operating Segments | Water Management
Segment Reporting Information, Additional Information [Abstract]
Net sales by product									$ 49.1	$ 45.9	$ 43.5