Short-Term Debt (Details) |
3 Months Ended | ||
|---|---|---|---|
|
Mar. 31, 2018
USD ($)
|
Mar. 21, 2018
USD ($)
|
Mar. 20, 2018
USD ($)
|
|
| American Water Capital Corp. | |||
| Short-term Debt [Line Items] | |||
| Line of credit facility, maximum borrowing capacity | $ 500,000,000 | ||
| 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 | $ 1,180,000,000 | ||
| Revolving Credit Facility | Letter of Credit | |||
| Short-term Debt [Line Items] | |||
| Line of credit facility, maximum borrowing capacity | 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 |