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Other Financial Data (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Apr. 28, 2017	Sep. 30, 2016
Liability for Catastrophe Claims [Line Items]
Asbestos insurance receivables	$ 133
Asbestos liabilities, gross	340		$ 52
Approximate annual rentals under noncancellable long-term leases, exclusive of maintenance, taxes, insurance and other operating costs, 2018	171
Approximate annual rentals under noncancellable long-term leases, exclusive of maintenance, taxes, insurance and other operating costs, 2019	125
Approximate annual rentals under noncancellable long-term leases, exclusive of maintenance, taxes, insurance and other operating costs, 2020	81
Approximate annual rentals under noncancellable long-term leases, exclusive of maintenance, taxes, insurance and other operating costs, 2021	49
Approximate annual rentals under noncancellable long-term leases, exclusive of maintenance, taxes, insurance and other operating costs, 2022	$ 31
Pentair's Valves & Controls [Member]
Liability for Catastrophe Claims [Line Items]
Asbestos insurance receivables		$ 95
Asbestos liabilities, gross		$ 240