Short-Term Debt (Details) |
3 Months Ended | 6 Months Ended | ||||
|---|---|---|---|---|---|---|
|
Jun. 30, 2018
USD ($)
|
Jun. 30, 2017 |
Jun. 30, 2018
USD ($)
|
Jun. 30, 2017 |
Mar. 21, 2018
USD ($)
|
Mar. 20, 2018
USD ($)
|
|
| American Water Capital Corp. | ||||||
| Short-term Debt [Line Items] | ||||||
| Line of credit facility, maximum borrowing capacity | $ 500,000,000 | $ 500,000,000 | ||||
| Number of extensions allowed under credit facility instances | 2 | |||||
| Number of extensions allowed under credit facility, duration | 1 year | |||||
| Commercial paper maximum borrowing capacity | $ 1,600,000,000 | $ 2,100,000,000 | ||||
| Commercial paper | $ 1,650,000,000 | $ 1,650,000,000 | ||||
| Interest rate | 2.34% | 1.24% | 2.15% | 1.14% | ||
| Revolving Credit Facility | Letter of Credit | ||||||
| Short-term Debt [Line Items] | ||||||
| Line of credit facility, maximum borrowing capacity | $ 150,000,000 | $ 150,000,000 | ||||
| Revolving Credit Facility | American Water Capital Corp. | ||||||
| Short-term Debt [Line Items] | ||||||
| Line of credit facility, maximum borrowing capacity | $ 2,250,000,000 | $ 1,750,000,000 | ||||
| Proceeds from lines of credit | $ 0 | |||||