Long-Term Debt Retired Through Sinking Fund Provisions, Optional Redemptions or Payments at Maturities (Details) - Debt retired during the year $ in Millions	6 Months Ended
	Jun. 30, 2016 USD ($)
Debt Instrument [Line Items]
Total retirements and redemptions	$ 13
Other American Water subsidiaries | Mandatorily redeemable preferred stock
Debt Instrument [Line Items]
Interest Rate	8.49%
Maturity Date, Maximum	2036
Total retirements and redemptions	$ 1
Fixed rate two | American Water Capital Corp. | Private activity bonds and government funded debt
Debt Instrument [Line Items]
Maturity Date, Minimum	2021	[1]
Maturity Date, Maximum	2031	[1]
Total retirements and redemptions	$ 1	[1]
Fixed rate two | Other American Water subsidiaries | Private activity bonds and government funded debt
Debt Instrument [Line Items]
Maturity Date, Minimum	2016
Maturity Date, Maximum	2041
Total retirements and redemptions	$ 11
Fixed rate two | Minimum | American Water Capital Corp. | Private activity bonds and government funded debt
Debt Instrument [Line Items]
Interest Rate	1.79%	[1]
Fixed rate two | Minimum | Other American Water subsidiaries | Private activity bonds and government funded debt
Debt Instrument [Line Items]
Interest Rate	0.00%
Fixed rate two | Maximum | American Water Capital Corp. | Private activity bonds and government funded debt
Debt Instrument [Line Items]
Interest Rate	2.90%	[1]
Fixed rate two | Maximum | Other American Water subsidiaries | Private activity bonds and government funded debt
Debt Instrument [Line Items]
Interest Rate	5.30%

[1] American Water Capital Corp., which is a wholly owned subsidiary of the Company, has a support agreement with the Company that, under certain circumstances, is the functional equivalent of a guarantee. This indebtedness is considered “debt” for purposes of this support agreement.