| **Pension Plans And Other Post-Retirement Benefits (Schedule Of Target Asset Allocations) (Details)** | 12 Months Ended |         |
|-------------------------------------------------------------------------------------------------------|-----------------|---------|
||
| Pension Benefits [Member]                                                                             |            |    |
| **Defined Benefit Plan Disclosure [Line Items]**                                                      |            |    |
| Target Allocation                                                                                     | 100.00%         |    |
| Percentage of Plan Assets                                                                             | 100.00%         | 100.00% |
| Other Postretirement Benefits [Member]                                                                |            |    |
| **Defined Benefit Plan Disclosure [Line Items]**                                                      |            |    |
| Target Allocation                                                                                     | 100.00%         |    |
| Percentage of Plan Assets                                                                             | 100.00%         | 100.00% |
| Domestic equities [Member] | Pension Benefits [Member]                                                |            |    |
| **Defined Benefit Plan Disclosure [Line Items]**                                                      |            |    |
| Target Allocation minimum                                                                             | 25.00%          |    |
| Target Allocation maximum                                                                             | 75.00%          |    |
| Percentage of Plan Assets                                                                             | 65.00%          | 63.00%  |
| Domestic equities [Member] | Other Postretirement Benefits [Member]                                   |            |    |
| **Defined Benefit Plan Disclosure [Line Items]**                                                      |            |    |
| Target Allocation minimum                                                                             | 25.00%          |    |
| Target Allocation maximum                                                                             | 75.00%          |    |
| Percentage of Plan Assets                                                                             | 52.00%          | 54.00%  |
| International equities [Member] | Pension Benefits [Member]                                           |            |    |
| **Defined Benefit Plan Disclosure [Line Items]**                                                      |            |    |
| Target Allocation minimum                                                                             | 0.00%           |    |
| Target Allocation maximum                                                                             | 10.00%          |    |
| Percentage of Plan Assets                                                                             | 6.00%           | 6.00%   |
| International equities [Member] | Other Postretirement Benefits [Member]                              |            |    |
| **Defined Benefit Plan Disclosure [Line Items]**                                                      |            |    |
| Target Allocation minimum                                                                             | 0.00%           |    |
| Target Allocation maximum                                                                             | 10.00%          |    |
| Percentage of Plan Assets                                                                             | 3.00%           | 2.00%   |
| Fixed income [Member] | Pension Benefits [Member]                                                     |            |    |
| **Defined Benefit Plan Disclosure [Line Items]**                                                      |            |    |
| Target Allocation minimum                                                                             | 25.00%          |    |
| Target Allocation maximum                                                                             | 50.00%          |    |
| Percentage of Plan Assets                                                                             | 19.00%          | 24.00%  |
| Fixed income [Member] | Other Postretirement Benefits [Member]                                        |            |    |
| **Defined Benefit Plan Disclosure [Line Items]**                                                      |            |    |
| Target Allocation minimum                                                                             | 25.00%          |    |
| Target Allocation maximum                                                                             | 50.00%          |    |
| Percentage of Plan Assets                                                                             | 25.00%          | 26.00%  |
| Alternative investments [Member] | Pension Benefits [Member]                                          |            |    |
| **Defined Benefit Plan Disclosure [Line Items]**                                                      |            |    |
| Target Allocation minimum                                                                             | 0.00%           |    |
| Target Allocation maximum                                                                             | 5.00%           |    |
| Percentage of Plan Assets                                                                             | 2.00%           | 3.00%   |
| Alternative investments [Member] | Other Postretirement Benefits [Member]                             |            |    |
| **Defined Benefit Plan Disclosure [Line Items]**                                                      |            |    |
| Target Allocation minimum                                                                             | 0.00%           |    |
| Target Allocation maximum                                                                             | 5.00%           |    |
| Percentage of Plan Assets                                                                             | 0.00%           | 0.00%   |
| Cash And Cash Equivalents [Member] | Pension Benefits [Member]                                        |            |    |
| **Defined Benefit Plan Disclosure [Line Items]**                                                      |            |    |
| Target Allocation minimum                                                                             | 0.00%           |    |
| Target Allocation maximum                                                                             | 20.00%          |    |
| Percentage of Plan Assets                                                                             | 8.00%           | 4.00%   |
| Cash And Cash Equivalents [Member] | Other Postretirement Benefits [Member]                           |            |    |
| **Defined Benefit Plan Disclosure [Line Items]**                                                      |            |    |
| Target Allocation minimum                                                                             | 0.00%           |    |
| Target Allocation maximum                                                                             | 20.00%          |    |
| Percentage of Plan Assets                                                                             | 20.00%          | 18.00%  |

| X                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
+ Details**Name:**us-gaap_DefinedBenefitPlanDisclosureLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Target allocation of investments of this type to total plan assets presented on a weighted average basis.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(i) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2446-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920
+ Details**Name:**us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations**Namespace Prefix:**us-gaap_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Target allocation maximum percentage of investments of this type to total plan assets presented on a weighted average basis.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(i) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2446-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920
+ Details**Name:**us-gaap_DefinedBenefitPlanTargetPlanAssetAllocationsRangeMaximum**Namespace Prefix:**us-gaap_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Target allocation minimum percentage of investments of this type to total plan assets presented on a weighted average basis.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(i) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2446-114920
+ Details**Name:**us-gaap_DefinedBenefitPlanTargetPlanAssetAllocationsRangeMinimum**Namespace Prefix:**us-gaap_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2446-114920Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920
+ Details**Name:**us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations**Namespace Prefix:**us-gaap_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_PensionPlansDefinedBenefitMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_EquitySecuritiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=wtr_InternationalEquitiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_DebtSecuritiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=wtr_AlternativeInvestmentsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_CashAndCashEquivalentsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |