Earnings Per Share (Calculations for EPS) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic and diluted net earnings per share:
Net income attributable to Xylem (in usd)		$ 115	$ 99	$ 194	$ 155
Shares
Weighted average common shares outstanding		179,770	179,571	179,814	179,557
Add: Participating securities	[1]	35	28	29	31
Weighted average common shares outstanding — Basic		179,805	179,599	179,843	179,588
Plus incremental shares from assumed conversions:
Weighted average common shares outstanding — Diluted		181,042	180,600	181,203	180,626
Basic earnings per share (usd per share)		$ 0.64	$ 0.55	$ 1.08	$ 0.87
Diluted earnings per share (usd per share)		$ 0.64	$ 0.55	$ 1.07	$ 0.86
Stock Options
Plus incremental shares from assumed conversions:
Dilutive effect of common shares	[2]	886	640	907	600
Restricted Stock
Plus incremental shares from assumed conversions:
Dilutive effect of common shares	[2]	351	362	453	438

[1] Restricted stock unit awards containing rights to non-forfeitable dividends that participate in undistributed earnings with common shareholders are considered participating securities for purposes of computing earnings per share.

[2] Incremental shares from stock options, restricted stock units and performance share units are computed by the treasury stock method. The weighted average shares listed below were not included in the computation of diluted earnings per share because to do so would have been anti-dilutive for the periods presented or were otherwise excluded under the treasury stock method. The treasury stock method calculates dilution assuming the exercise of all in-the-money options and vesting of restricted stock units and performance share units, reduced by the repurchase of shares with the proceeds from the assumed exercises and unrecognized compensation expense for outstanding awards. Performance share units will be included in the treasury stock calculation of diluted earnings per share upon achievement of underlying performance or market conditions at the end of the reporting period. See Note 15, "Share-Based Compensation Plans" to the condensed consolidated financial statements for further detail on the performance share units.