Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	CASH ACCOUNT TRUST
Prospectus Date	rr_ProspectusDate	Aug. 01, 2012
DWS Government Cash Institutional Shares | Government & Agency Securities Portfolio
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Government & Agency Securities Portfolio
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The fund seeks to provide maximum current income consistent with stability of capital.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	These are the fees and expenses you may pay when you buy and hold shares.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	SHAREHOLDER FEES (paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a % of the value of your investment)
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This Example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategy
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	The fund is managed in accordance with Rule 2a-7 under the Investment Company Act of 1940, as amended, which governs the quality, maturity, diversity and liquidity of instruments in which a money fund may invest. The fund pursues its objective by investing exclusively in the following types of investments: US Treasury bills, notes, bonds and other obligations issued or guaranteed by the US government, its agencies or instrumentalities. Repurchase agreements backed by these securities. In a repurchase agreement, the fund buys securities at one price with a simultaneous agreement to sell back the securities at a future date at an agreed-upon price. The fund may invest in floating and variable rate instruments (obligations that do not bear interest at fixed rates). Working in consultation with portfolio management, a credit team screens potential securities and develops a list of those that the fund may buy. Portfolio management, looking for attractive yield and weighing considerations such as credit quality, economic outlooks and possible interest rate movements, then decides which securities on this list to buy.
Risk [Heading]	rr_RiskHeading	Main Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	There are several risk factors that could reduce the yield you get from the fund, cause the fund's performance to trail that of other investments, or cause you to lose money. Money market fund risk. An investment in the fund is not insured or guaranteed by the FDIC or any other government agency. Although the fund seeks to preserve the value of your investment at $1.00 per share, this share price isn't guaranteed, and if it falls below $1.00 you would lose money. The Advisor is not obligated to take any action to maintain the $1.00 share price. The share price could fall below $1.00 as a result of the actions of one or more large investors in the fund. The credit quality of the fund's holdings can change rapidly in certain markets, and the default of a single holding could cause the fund's share price to fall below $1.00, as could periods of high redemption pressures and/or illiquid markets. Interest rate risk. Rising interest rates could cause the value of the fund's investments — and therefore its share price as well — to decline. Conversely, any decline in interest rates is likely to cause the fund's yield to decline, and during periods of unusually low interest rates, the fund's yield may approach zero. Over time, the total return of a money market fund may not keep pace with inflation, which could result in a net loss of purchasing power for long-term investors. Security selection risk. Although short-term securities are relatively stable investments, it is possible that the securities in which the fund invests will not perform as expected. This could cause the fund's returns to lag behind those of similar money market mutual funds and could result in a decline in share price. Repurchase agreement risk. If the party that sells the securities to the fund defaults on its obligation to repurchase them at the agreed-upon time and price, the fund could lose money. Counterparty risk. A financial institution or other counterparty with whom the fund does business, or that underwrites, distributes or guarantees any investments or contracts that the fund owns or is otherwise exposed to, may decline in financial health and become unable to honor its commitments. This could cause losses for the fund or could delay the return or delivery of collateral or other assets to the fund. Credit risk. The fund's performance could be hurt if an issuer of a money market instrument suffers an adverse change in financial condition that results in a payment default, security downgrade or inability to meet a financial obligation. Some securities issued by US government agencies or instrumentalities are backed by the full faith and credit of the US government. Others are supported only by the credit of that agency or instrumentality. For this latter group, if there is a potential or actual loss of principal and interest on these securities, the US government might provide financial support, but has no obligation to do so. Because of the rising US government debt burden, it is possible that the US government may not be able to meet its financial obligations or that securities issued by the US government may experience credit downgrades. Such a credit event may also adversely impact the financial markets. Prepayment and extension risk. When interest rates fall, issuers of high interest debt obligations may pay off the debts earlier than expected (prepayment risk), and the fund may have to reinvest the proceeds at lower yields. When interest rates rise, issuers of lower interest debt obligations may pay off the debts later than expected (extension risk), thus keeping the fund's assets tied up in lower interest debt obligations. Ultimately, any unexpected behavior in interest rates could increase the volatility of the fund's yield and could hurt fund performance. Prepayments could also create capital gains tax liability in some instances.
Risk Lose Money [Text]	rr_RiskLoseMoney	There are several risk factors that could reduce the yield you get from the fund, cause the fund's performance to trail that of other investments, or cause you to lose money.
Risk Money Market Fund [Text]	rr_RiskMoneyMarketFund	Money market fund risk. An investment in the fund is not insured or guaranteed by the FDIC or any other government agency. Although the fund seeks to preserve the value of your investment at $1.00 per share, this share price isn't guaranteed, and if it falls below $1.00 you would lose money. The Advisor is not obligated to take any action to maintain the $1.00 share price. The share price could fall below $1.00 as a result of the actions of one or more large investors in the fund. The credit quality of the fund's holdings can change rapidly in certain markets, and the default of a single holding could cause the fund's share price to fall below $1.00, as could periods of high redemption pressures and/or illiquid markets.
Risk Not Insured Depository Institution [Text]	rr_RiskNotInsuredDepositoryInstitution	An investment in the fund is not insured or guaranteed by the FDIC or any other government agency.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Past Performance
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	How a fund's returns vary from year to year can give an idea of its risk. Past performance may not indicate future results. All performance figures below assume that dividends were reinvested. The 7-day yield, which is often referred to as the "current yield," is the income generated by the fund over a seven-day period. This amount is then annualized, which means that we assume the fund generates the same income every week for a year. For more recent performance figures and the current yield, go to www.dbadvisorsliquidity.com/US (the Web site does not form a part of this prospectus) or call the phone number for your share class included in this prospectus.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	How a fund's returns vary from year to year can give an idea of its risk.
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.dbadvisorsliquidity.com/US
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	Past performance may not indicate future results.
Bar Chart [Heading]	rr_BarChartHeading	CALENDAR YEAR TOTAL RETURNS (%) (DWS Government Cash Institutional Shares)
Bar Chart Narrative [Text Block]	rr_BarChartNarrativeTextBlock	Returns for other classes were different and are not shown here.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Best Quarter: 0.90%, Q1 2008 Worst Quarter: 0.01%, Q4 2011 Year-to-Date as of 6/30/12: 0.01%
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (for periods ended 12/31/2011 expressed as a %)
Performance Table Closing [Text Block]	rr_PerformanceTableClosingTextBlock	Total returns would have been lower if operating expenses hadn't been reduced. For more recent performance information, contact the financial services firm from which you obtained this prospectus.
DWS Government Cash Institutional Shares | Government & Agency Securities Portfolio | DWS Government Cash Institutional Shares
Risk/Return:	rr_RiskReturnAbstract
SHAREHOLDER FEES (paid directly from your investment)	rr_ShareholderFeeOther	none
Management fee	rr_ManagementFeesOverAssets	0.05%
Distribution/Service (12b-1) fees	rr_DistributionAndService12b1FeesOverAssets	none
Other expenses	rr_OtherExpensesOverAssets	0.14%
Total annual fund operating expenses	rr_ExpensesOverAssets	0.19%
1 Year	rr_ExpenseExampleYear01	19
3 Years	rr_ExpenseExampleYear03	61
5 Years	rr_ExpenseExampleYear05	107
10 Years	rr_ExpenseExampleYear10	243
2008	rr_AnnualReturn2008	2.41%
2009	rr_AnnualReturn2009	0.31%
2010	rr_AnnualReturn2010	0.06%
2011	rr_AnnualReturn2011	0.05%
Year to Date Return, Label	rr_YearToDateReturnLabel	Year-to-Date
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Jun. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	0.01%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Mar. 31, 2008
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	0.90%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.01%
Class Inception	rr_AverageAnnualReturnInceptionDate	Feb. 16, 2007
1 Year	rr_AverageAnnualReturnYear01	0.05%
Since Inception	rr_AverageAnnualReturnSinceInception	1.48%