Business Segment Information - Schedule of Business Segment Information (Details) $ in Millions	3 Months Ended								9 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2018 segment	Mar. 31, 2019 USD ($) segment	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of business segments | segment									2	2
Segment Reporting Information, Additional Information [Abstract]
Net sales by product	$ 537.5	$ 485.0	$ 524.8	$ 503.6	$ 517.9	$ 436.7	$ 453.8	$ 443.2		$ 2,050.9	$ 1,851.6	$ 1,712.5
Income (loss) from operations										305.6	266.4	203.2
Non-operating expense:
Interest expense, net										(69.9)	(75.1)	(88.3)
Gain (loss) on the extinguishment of debt										4.3	(11.9)	(7.8)
Other (expense) income, net										(1.2)	7.7	0.2
Income from continuing operations before income taxes										238.8	187.1	107.3
(Provision) benefit for income taxes										53.4	(19.5)	15.6
Equity method investment income										3.6	0.0	0.0
Net income from continuing operations	47.7	52.9	46.2	42.2	58.0	85.9	33.3	29.4		189.0	206.6	91.7
Loss from discontinued operations, net of tax	(0.4)	(27.8)	(83.7)	(42.8)	(119.9)	(4.3)	(3.5)	(2.9)		(154.7)	(130.6)	(17.6)
Net income (loss)	47.3	25.1	(37.5)	(0.6)	(61.9)	81.6	29.8	26.5		34.3	76.0	74.1
Non-controlling interest income	0.1	(0.3)	0.1	0.1	0.1	0.0	0.0	0.0		0.0	0.1	0.0
Net income (loss) attributable to Rexnord	47.2	25.4	(37.6)	(0.7)	(62.0)	81.6	29.8	26.5		34.3	75.9	74.1
Dividends on preferred stock	(5.8)	(5.8)	(5.8)	(5.8)	(5.8)	(5.8)	(5.8)	(5.8)		(23.2)	(23.2)	(7.3)
Net income (loss) attributable to Rexnord common stockholders	41.4	$ 19.6	$ (43.4)	$ (6.5)	(67.8)	$ 75.8	$ 24.0	$ 20.7		11.1	52.7	66.8
Depreciation and Amortization										87.9	79.7	96.1
Capital Expenditures										42.5	38.0	50.8
Total Assets	3,259.7				3,423.7					3,259.7	3,423.7	3,539.3
Segments, Geographical Areas [Abstract]
Net Sales										2,050.9	1,851.6	1,712.5
Long-lived Assets	383.0				396.5					383.0	396.5	341.5
United States
Segments, Geographical Areas [Abstract]
Net Sales										1,460.6	1,361.6	1,285.1
Long-lived Assets	260.7				260.9					260.7	260.9	261.9
Europe
Segments, Geographical Areas [Abstract]
Net Sales										327.5	255.5	218.9
Long-lived Assets	78.9				91.2					78.9	91.2	37.7
Rest of World
Segments, Geographical Areas [Abstract]
Net Sales										262.8	234.5	208.5
Long-lived Assets	43.4				44.4					43.4	44.4	41.9
Process & Motion Control
Segment Reporting Information, Additional Information [Abstract]
Net sales by product										1,380.6	1,241.2	1,134.7
Process & Motion Control | Europe
Segment Reporting Information, Additional Information [Abstract]
Net sales by product										327.5	255.5	218.9
Water Management
Segment Reporting Information, Additional Information [Abstract]
Net sales by product										670.3	610.4	577.8
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										226.1	191.3	133.0
Non-operating expense:
Depreciation and Amortization										63.0	56.0	69.9
Capital Expenditures										36.3	34.2	42.0
Total Assets	2,677.7				2,598.8					2,677.7	2,598.8	2,671.4
Operating Segments | Water Management
Segment Reporting Information, Additional Information [Abstract]
Income (loss) from operations										139.7	125.7	112.3
Non-operating expense:
Depreciation and Amortization										24.9	23.7	26.2
Capital Expenditures										6.2	3.8	8.8
Total Assets	576.8				820.9					576.8	820.9	862.3
Corporate
Segment Reporting Information, Additional Information [Abstract]
Income (loss) from operations										(60.2)	(50.6)	(42.1)
Non-operating expense:
Total Assets	$ 5.2				$ 4.0					5.2	4.0	5.6
Original equipment manufacturers/ end-users | Process & Motion Control
Segment Reporting Information, Additional Information [Abstract]
Net sales by product										768.5	690.5	594.6
Original equipment manufacturers/ end-users | Operating Segments | Process & Motion Control
Segment Reporting Information, Additional Information [Abstract]
Net sales by product										768.5	690.5	594.6
Maintenance, repair, and operations | Process & Motion Control
Segment Reporting Information, Additional Information [Abstract]
Net sales by product										612.1	550.7	540.1
Maintenance, repair, and operations | Operating Segments | Process & Motion Control
Segment Reporting Information, Additional Information [Abstract]
Net sales by product										612.1	550.7	540.1
Water safety, quality, flow control and conservation | Water Management
Segment Reporting Information, Additional Information [Abstract]
Net sales by product										624.4	566.9	538.9
Water safety, quality, flow control and conservation | Operating Segments | Water Management
Segment Reporting Information, Additional Information [Abstract]
Net sales by product										624.4	566.9	538.9
Water infrastructure | Water Management
Segment Reporting Information, Additional Information [Abstract]
Net sales by product										45.9	43.5	38.9
Water infrastructure | Operating Segments | Water Management
Segment Reporting Information, Additional Information [Abstract]
Net sales by product										$ 45.9	$ 43.5	$ 38.9