Postretirement Benefit Plans - Additional Information (Detail) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) Participant shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Company contributions to defined contribution plans	$ 10.6	$ 17.6	$ 17.1
Shares of ITT Stock Held in Defined Contribution Plan | shares	0.1
Active participants in numerous defined benefit pension plans | Participant	900
Settlement charges	$ 137.0	0.0	1.7
Accumulated benefit obligation	$ 121.6	406.3
Assumed rate of future decrease in per capita cost of health care for 2028	4.50%
Contributions to postretirement plans	$ 18.0	22.9	11.2
Employer contributions	18.0	22.9
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement charges	137.0	0.0	1.7
Contributions to postretirement plans	13.4	12.9
Discretionary Pension Contribution		9.0
Defined Benefit Plan, Expected Employer Contributions Next Fiscal Year	6.0
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	4.6	10.0
Defined Benefit Plan, Expected Employer Contributions Next Fiscal Year	$ 9.0
International Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected Benefit Obligation	88.00%
International Plan [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement charges	$ 0.1	0.0	$ 0.0
Employer contributions	4.1	3.0
United States | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement charges	136.9	0.0
Employer contributions	$ 9.3	$ 9.9
Pre Age Sixty Five [Member]
Defined Benefit Plan Disclosure [Line Items]
Assumed rate of future increase in per capita cost of health care for 2021	6.50%
Post-age 65 retirees [Member]
Defined Benefit Plan Disclosure [Line Items]
Assumed rate of future increase in per capita cost of health care for 2021	5.80%
U.S. Qualified Plan Termination [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets Used to Fund Settlement	$ 320.0
Contributions to postretirement plans	$ 8.4