Components of Long-Term Debt (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Debt Instrument [Line Items]
Long-term debt	$ 5,200,132		$ 5,203,524
Unamortized debt, net	35,012	[1]	35,984	[1]
Fair value adjustment to interest rate hedge	4,396		4,724
Total long-term debt	5,239,540		5,244,232
American Water Capital Corp. ("AWCC") | Private activity bonds and government funded debt | Long-term debt | Fixed rate
Debt Instrument [Line Items]
Interest Rate, Minimum	2.30%	[2]
Interest Rate, Maximum	6.75%	[2]
Weighted Average Rate	5.63%	[2]
Maturity Date, Minimum	2018	[2]
Maturity Date, Maximum	2040	[2]
Long-term debt	330,732	[2]	330,732	[2]
American Water Capital Corp. ("AWCC") | Senior notes | Long-term debt | Fixed rate
Debt Instrument [Line Items]
Interest Rate, Minimum	3.85%	[2]
Interest Rate, Maximum	8.27%	[2]
Weighted Average Rate	5.69%	[2]
Maturity Date, Minimum	2016	[2]
Maturity Date, Maximum	2042	[2]
Long-term debt	3,312,757	[2]	3,312,761	[2]
Other subsidiaries | Private activity bonds and government funded debt | Long-term debt | Fixed rate
Debt Instrument [Line Items]
Interest Rate, Minimum	0.00%
Interest Rate, Maximum	6.20%
Weighted Average Rate	4.69%
Maturity Date, Minimum	2014
Maturity Date, Maximum	2041
Long-term debt	861,535		863,716
Other subsidiaries | Mortgage bonds | Long-term debt | Fixed rate
Debt Instrument [Line Items]
Interest Rate, Minimum	4.29%
Interest Rate, Maximum	9.71%
Weighted Average Rate	7.41%
Maturity Date, Minimum	2015
Maturity Date, Maximum	2039
Long-term debt	676,500		676,500
Other subsidiaries | Mandatorily redeemable preferred stock | Long-term debt
Debt Instrument [Line Items]
Interest Rate, Minimum	8.47%
Interest Rate, Maximum	9.75%
Weighted Average Rate	8.61%
Maturity Date, Minimum	2019
Maturity Date, Maximum	2036
Long-term debt	17,702		18,902
Other subsidiaries | Capital lease obligation | Long-term debt
Debt Instrument [Line Items]
Interest Rate, Minimum	12.17%
Weighted Average Rate	12.17%
Maturity Date, Maximum	2026
Long-term debt	$ 906		$ 913

[1] Primarily fair value adjustments previously recognized in acquisition purchase accounting.

[2] AWCC, which is a wholly-owned subsidiary of the Company, has a strong support agreement with its parent that, under certain circumstances, is the functional equivalent of a guarantee.