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Consolidated Statements Of Capitalization (Parenthetical) (USD $)
 3 Months Ended 12 Months Ended
Mar. 31, 2015
Dec. 31, 2014
Common stock, par value 0.5us-gaap_CommonStockParOrStatedValuePerShare 0.5us-gaap_CommonStockParOrStatedValuePerShare
Long-Term Debt Of Subsidiaries 0.00% To 0.99% [Member]    
Interest rate range, minimum 0.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
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Interest rate range, maximum 0.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
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= wtr_LongTermDebtOfSubsidiariesZeroPointZeroZeroPercentageToZeroPointNineNinePercentageMember
Maturity date range, start 2023 2023
Maturity date range, end 2033 2033
Long-Term Debt Of Subsidiaries 1.00% To 1.99% [Member]    
Interest rate range, minimum 1.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
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Interest rate range, maximum 1.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
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Maturity date range, start 2016 2016
Maturity date range, end 2035 2035
Long-Term Debt Of Subsidiaries 2.00% To 2.99% [Member]    
Interest rate range, minimum 2.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
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Interest rate range, maximum 2.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
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= wtr_LongTermDebtOfSubsidiariesTwoPointZeroZeroPercentageToTwoPointNineNinePercentageMember
Maturity date range, start 2024 2024
Maturity date range, end 2031 2031
Long-Term Debt Of Subsidiaries 3.00% To 3.99% [Member]    
Interest rate range, minimum 3.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
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= wtr_LongTermDebtOfSubsidiariesThreePointZeroZeroPercentageToThreePointNineNinePercentageMember
Interest rate range, maximum 3.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
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= wtr_LongTermDebtOfSubsidiariesThreePointZeroZeroPercentageToThreePointNineNinePercentageMember		 3.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
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= wtr_LongTermDebtOfSubsidiariesThreePointZeroZeroPercentageToThreePointNineNinePercentageMember
Maturity date range, start 2016 2016
Maturity date range, end 2047 2047
Long-Term Debt Of Subsidiaries 4.00% To 4.99% [Member]    
Interest rate range, minimum 4.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
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Interest rate range, maximum 4.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
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= wtr_LongTermDebtOfSubsidiariesFourPointZeroZeroPercentageToFourPointNineNinePercentageMember
Maturity date range, start 2020 2020
Maturity date range, end 2054 2054
Long-Term Debt Of Subsidiaries 5.00% To 5.99% [Member]    
Interest rate range, minimum 5.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
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Interest rate range, maximum 5.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
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= wtr_LongTermDebtOfSubsidiariesFivePointZeroZeroPercentageToFivePointNineNinePercentageMember
Maturity date range, start 2015 2015
Maturity date range, end 2043 2043
Long-Term Debt Of Subsidiaries 6.00% To 6.99% [Member]    
Interest rate range, minimum 6.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
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Interest rate range, maximum 6.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
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Maturity date range, start 2015 2015
Maturity date range, end 2036 2036
Long-Term Debt Of Subsidiaries 7.00% To 7.99% [Member]    
Interest rate range, minimum 7.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
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Interest rate range, maximum 7.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
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= wtr_LongTermDebtOfSubsidiariesSevenPointZeroZeroPercentageToSevenPointNineNinePercentageMember
Maturity date range, start 2022 2022
Maturity date range, end 2027 2027
Long-Term Debt Of Subsidiaries 8.00% To 8.99% [Member]    
Interest rate range, minimum 8.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
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= wtr_LongTermDebtOfSubsidiariesEightPointZeroZeroPercentageToEightPointNineNinePercentageMember
Interest rate range, maximum 8.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
/ us-gaap_DebtInstrumentAxis
= wtr_LongTermDebtOfSubsidiariesEightPointZeroZeroPercentageToEightPointNineNinePercentageMember		 8.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
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= wtr_LongTermDebtOfSubsidiariesEightPointZeroZeroPercentageToEightPointNineNinePercentageMember
Maturity date range, start 2021 2021
Maturity date range, end 2025 2025
Long-Term Debt Of Subsidiaries 9.00% To 9.99% [Member]    
Interest rate range, minimum 9.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
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= wtr_LongTermDebtOfSubsidiariesNinePointZeroZeroPercentageToNinePointNineNinePercentageMember		 9.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
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Interest rate range, maximum 9.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
/ us-gaap_DebtInstrumentAxis
= wtr_LongTermDebtOfSubsidiariesNinePointZeroZeroPercentageToNinePointNineNinePercentageMember		 9.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
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Maturity date range, start 2018 2018
Maturity date range, end 2026 2026
Long-Term Debt Of Subsidiaries 10.00% To 10.99% [Member]    
Interest rate range, minimum 10.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
/ us-gaap_DebtInstrumentAxis
= wtr_LongTermDebtOfSubsidiariesTenPointZeroZeroPercentageToTenPointNineNinePercentageMember		 10.00%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
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Interest rate range, maximum 10.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
/ us-gaap_DebtInstrumentAxis
= wtr_LongTermDebtOfSubsidiariesTenPointZeroZeroPercentageToTenPointNineNinePercentageMember		 10.99%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
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= wtr_LongTermDebtOfSubsidiariesTenPointZeroZeroPercentageToTenPointNineNinePercentageMember
Maturity date 2018 2018
Bank Note at 1.921% due 2017 [Member]    
Interest rate 1.921%us-gaap_DebtInstrumentInterestRateStatedPercentage
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= wtr_BankNoteAtOnePointNineTwoOnePercentMember		 1.921%us-gaap_DebtInstrumentInterestRateStatedPercentage
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= wtr_BankNoteAtOnePointNineTwoOnePercentMember
Maturity date 2017 2017
Notes at 3.57% due 2027 [Member]    
Interest rate 3.57%us-gaap_DebtInstrumentInterestRateStatedPercentage
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= wtr_NotesAtThreePointFiveSevenPercentMember		 3.57%us-gaap_DebtInstrumentInterestRateStatedPercentage
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Maturity date 2027 2027
Notes Ranging From 4.62% To 4.87%, due 2016 through 2024 [Member]    
Interest rate range, minimum 4.62%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
/ us-gaap_DebtInstrumentAxis
= wtr_NotesRangingFromFourPointSixTwoPercentageToFourPointEightSevenPercentageMember		 4.62%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
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Interest rate range, maximum 4.87%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
/ us-gaap_DebtInstrumentAxis
= wtr_NotesRangingFromFourPointSixTwoPercentageToFourPointEightSevenPercentageMember		 4.87%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
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Maturity date range, start 2016 2016
Maturity date range, end 2024 2024
Notes Ranging From 5.20% To 5.95%, due 2016 through 2037 [Member]    
Interest rate range, minimum 5.20%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMinimum
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Interest rate range, maximum 5.83%us-gaap_DebtInstrumentInterestRateStatedPercentageRateRangeMaximum
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Maturity date range, start 2016 2016
Maturity date range, end 2037 2037