Restructuring Charges (Estimated Restructuring Costs) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
2019 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	$ 11
Restructuring costs incurred during period	6
Total expected costs remaining	5
2018 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	17
Restructuring costs incurred during period	1	$ 15
Total expected costs remaining	1
2017 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	28
Restructuring costs incurred during period	1	4	$ 11
Total expected costs remaining	12
Operating Segments | Water Infrastructure | 2019 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	5
Restructuring costs incurred during period	3
Total expected costs remaining	2
Operating Segments | Water Infrastructure | 2018 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	9
Restructuring costs incurred during period	1	7
Total expected costs remaining	1
Operating Segments | Water Infrastructure | 2017 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	16
Restructuring costs incurred during period	0	2	5
Total expected costs remaining	9
Operating Segments | Applied Water | 2019 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	0
Restructuring costs incurred during period	0
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	8
Restructuring costs incurred during period	0	1	4
Total expected costs remaining	3
Operating Segments | Measurement & Control Solutions | 2019 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	6
Restructuring costs incurred during period	3
Total expected costs remaining	3
Operating Segments | Measurement & Control Solutions | 2018 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	7
Restructuring costs incurred during period	0	7
Total expected costs remaining	0
Operating Segments | Measurement & Control Solutions | 2017 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	4
Restructuring costs incurred during period	1	1	2
Total expected costs remaining	0
Corporate | 2019 Plan
Restructuring Cost and Reserve [Line Items]
Total expected costs	0
Restructuring costs incurred during period	0
Total expected costs remaining	0
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