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v3.19.1

23. Knowledge retention program (Details) | 12 Months Ended
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Dec. 31, 2018
More than 15 years |
SummaryOfKnowledgeRetentionProgramLineItems [Line Items] |
Percent of the Guarantee Fund for Length of Service (FGTS) | 40.00%
11 - 15 years |
SummaryOfKnowledgeRetentionProgramLineItems [Line Items] |
Percent of the Guarantee Fund for Length of Service (FGTS) | 30.00%
6 - 10 years |
SummaryOfKnowledgeRetentionProgramLineItems [Line Items] |
Percent of the Guarantee Fund for Length of Service (FGTS) | 15.00%
0 - 5 years |
SummaryOfKnowledgeRetentionProgramLineItems [Line Items] |
Percent of the Guarantee Fund for Length of Service (FGTS) | 5.00%

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Namespace Prefix: | SBS_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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Namespace Prefix: | SBS_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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Name: | srt_RangeAxis=SBS_MoreThanFifteenYearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
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- Details
Name: | srt_RangeAxis=SBS_ElevenToFifteenYearsMember
Namespace Prefix: |
Data Type: | na
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Period Type: |

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- Details
Name: | srt_RangeAxis=SBS_SixToTenYearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=SBS_ZeroToFiveYearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |