Short-Term Debt - Schedule of Short-Term Borrowings Activity (Details) - American Water Capital Corp. - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
|
| Short-term Debt [Line Items] | ||
| Average borrowings | $ 726 | $ 1,029 |
| Maximum borrowings outstanding | $ 1,271 | $ 1,905 |
| Weighted average interest rates, computed on daily basis | 2.54% | 2.28% |
| Weighted average interest rates, as of December 31 | 1.86% | 2.84% |