American Water Works Company, Inc. - 10-K filing on 2020-02-18

Revenue Recognition - Disaggregated Revenues (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									$ 3,587
Other operating income									23
Operating revenues	$ 902	$ 1,013	$ 882	$ 813	$ 850	$ 976	$ 853	$ 761	3,610	$ 3,440	$ 3,357
Service, Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									(22)
Other operating income									(1)
Operating revenues									(23)
Regulated Businesses
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									3,070
Other operating income									24
Alternative revenue programs									16
Lease contract revenue									7
Operating revenues									3,094
Regulated Businesses \| Water Services
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									2,867
Other operating income									1
Operating revenues									2,868
Regulated Businesses \| Water Services \| Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									1,734
Other operating income									1
Operating revenues									1,735
Regulated Businesses \| Water Services \| Commercial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									639
Other operating income									0
Operating revenues									639
Regulated Businesses \| Water Services \| Fire Service
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									142
Operating revenues									142
Regulated Businesses \| Water Services \| Industrial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									138
Operating revenues									138
Regulated Businesses \| Water Services \| Public and Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									214
Other operating income									0
Operating revenues									214
Regulated Businesses \| Wastewater Services
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									167
Operating revenues									167
Regulated Businesses \| Wastewater Services \| Residential
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									119
Operating revenues									119
Regulated Businesses \| Wastewater Services \| Commercial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									31
Operating revenues									31
Regulated Businesses \| Wastewater Services \| Industrial
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									3
Operating revenues									3
Regulated Businesses \| Wastewater Services \| Public and Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									14
Operating revenues									14
Regulated Businesses \| Miscellaneous Utility Charge
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									36
Operating revenues									36
Market-Based Businesses
Disaggregation of Revenue [Line Items]
Revenue from contract with customer									539
Operating revenues									$ 539