Long-Term Debt - Issued (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Total issuances	$ 1,264	$ 822	$ 1,118
Other American Water subsidiaries | Private activity bonds and government funded debt—fixed rate | Fixed rate
Debt Instrument [Line Items]
Total issuances	$ 143
Other American Water subsidiaries | Private activity bonds and government funded debt—fixed rate | Fixed rate | Minimum
Debt Instrument [Line Items]
Rate	0.00%
Other American Water subsidiaries | Private activity bonds and government funded debt—fixed rate | Fixed rate | Maximum
Debt Instrument [Line Items]
Rate	3.75%
Other American Water subsidiaries | Private activity bonds and government funded debt—fixed rate | Fixed rate | Weighted Average
Debt Instrument [Line Items]
Rate	2.88%
American Water Capital Corp. (AWCC) | Senior notes—fixed rate | Fixed rate
Debt Instrument [Line Items]
Rate	3.63%
Total issuances	$ 1,035
American Water Capital Corp. (AWCC) | Senior notes—fixed rate | Fixed rate | Weighted Average
Debt Instrument [Line Items]
Rate	3.63%
American Water Capital Corp. (AWCC) | Private activity bonds and government funded debt—fixed rate | Fixed rate
Debt Instrument [Line Items]
Total issuances	$ 86
American Water Capital Corp. (AWCC) | Private activity bonds and government funded debt—fixed rate | Fixed rate | Minimum
Debt Instrument [Line Items]
Rate	3.70%
American Water Capital Corp. (AWCC) | Private activity bonds and government funded debt—fixed rate | Fixed rate | Maximum
Debt Instrument [Line Items]
Rate	3.88%
American Water Capital Corp. (AWCC) | Private activity bonds and government funded debt—fixed rate | Fixed rate | Weighted Average
Debt Instrument [Line Items]
Rate	3.80%