FINANCIAL INSTRUMENTS AND RISK MANAGEMENT - Interest Rate Exposures (Details) - Interest rate risk - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Risk management
Percentage of increase in risk variable used for sensitivity analysis	1.00%
Percentage of decrease in risk variable used for sensitivity analysis	1.00%
Increase in annual net interest charge that would result from increased interest rate, per sensitivity analysis	$ 3	$ 6

The increase (decrease) in annual net interest charge as a result of an increase in the relevant risk variable that was reasonably possible at the end of the reporting period.

No definition available.

Name:	snn_IncreaseDecreaseInAnnualNetInterestChargeDueToReasonablyPossibleIncreaseInRiskVariable
Namespace Prefix:	snn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant