Restructuring Charges (Estimated Restructuring Costs) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
2018 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	$ 17
Restructuring costs incurred during period	4	$ 8
Total expected costs remaining	5
2017 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	33
Restructuring costs incurred during period	1	1	$ 11
Total expected costs remaining	20
2016 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	40
Restructuring costs incurred during period	0	1	9	$ 29
Total expected costs remaining	1
Operating Segments | Water Infrastructure | 2018 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	8
Restructuring costs incurred during period	2	2
Total expected costs remaining	4
Operating Segments | Water Infrastructure | 2017 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	19
Restructuring costs incurred during period	1	1	5
Total expected costs remaining	12
Operating Segments | Water Infrastructure | 2016 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	13
Restructuring costs incurred during period	0	0	2	11
Total expected costs remaining	0
Operating Segments | Applied Water | 2018 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	1
Restructuring costs incurred during period	0	1
Total expected costs remaining	0
Operating Segments | Applied Water | 2017 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	12
Restructuring costs incurred during period	0	0	4
Total expected costs remaining	8
Operating Segments | Applied Water | 2016 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	14
Restructuring costs incurred during period	0	0	4	10
Total expected costs remaining	0
Operating Segments | Measurement & Control Solutions | 2018 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	8
Restructuring costs incurred during period	2	5
Total expected costs remaining	1
Operating Segments | Measurement & Control Solutions | 2017 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	2
Restructuring costs incurred during period	0	0	2
Total expected costs remaining	0
Operating Segments | Measurement & Control Solutions | 2016 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	11
Restructuring costs incurred during period	0	1	3	6
Total expected costs remaining	1
Corporate | 2018 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	0
Restructuring costs incurred during period	0	0
Total expected costs remaining	0
Corporate | 2017 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	0
Restructuring costs incurred during period	0	0	0
Total expected costs remaining	0
Corporate | 2016 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	2
Restructuring costs incurred during period	0	$ 0	$ 0	$ 2
Total expected costs remaining	$ 0