Untitled Document

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

T. Rowe Price Institutional Income Funds, Inc.

Prospectus Date

rr_ProspectusDate

Oct. 01, 2012

Institutional Class | T. Rowe Price Institutional Core Plus Fund

Objective, Primary [Text Block]

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

T. Rowe Price

Institutional Core Plus Fund

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

rr_ObjectivePrimaryTextBlock

The fund seeks to maximize total return through income and capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Fees and Expenses of the Fund

Annual fund operating expenses
(expenses that you pay each year as a
percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

140.60%

Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]

rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees

The figure shown under “Total annual fund operating expenses after fee waiver/expense reimbursement” does not match the “Ratio of expenses to average net assets” shown in the Financial Highlights table, as that figure does not include acquired fund fees and expenses.

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

Strategy [Heading]

rr_StrategyHeading

Investments, Risks, and Performance

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

As with any mutual fund, there is no guarantee that the fund will achieve its objective. The fund’s share price fluctuates, which means you could lose money by investing in the fund. The principal risks of investing in this fund are summarized as follows:

Active management risk The fund is subject to the risk that the investment adviser’s judgments about the attractiveness, value, or potential appreciation of the fund’s investments may prove to be incorrect. If the securities selected and strategies employed by the fund fail to produce the intended results, the fund could underperform other funds with similar objectives and investment strategies.

Interest rate risk This is the risk that a rise in interest rates will cause the price of a fixed rate debt security to fall. Generally, securities with longer maturities and funds with longer weighted average maturities carry greater interest rate risk.

Credit risk This is the risk that an issuer of a debt security could suffer an adverse change in financial condition that results in a payment default, security downgrade, or inability to meet a financial obligation. The fund’s exposure to credit risk is increased to the extent the fund invests in noninvestment-grade “junk” bonds. Junk bonds should be considered speculative as they carry greater risk of default and erratic price swings due to adverse changes in the credit quality of the issuer.

Liquidity risk This is the risk that the fund may not be able to sell a holding in a timely manner at a desired price.

Foreign investing risk This is the risk that the fund’s investments in foreign securities may be adversely affected by political and economic conditions overseas, reduced liquidity, or decreases in foreign currency values relative to the U.S. dollar. These risks are heightened for the fund’s investments in emerging markets. Any attempts at hedging currencies may not be successful and could cause the fund to lose money.

Prepayment risk and extension risk Prepayment risk is the risk that the principal on mortgage-backed securities, other asset-backed securities or any debt security with an embedded call option may be prepaid at any time, which could reduce yield and market value. The rate of prepayments tends to increase as interest rates fall, which could cause the average maturity of the portfolio to shorten. Extension risk may result from a rise in interest rates, which tends to make mortgage-backed securities, asset-backed securities, and other callable debt securities more volatile.

Derivatives risk To the extent the fund uses interest rate futures and forward currency exchange contracts, it is exposed to additional volatility in comparison to investing directly in bonds and other debt securities. These instruments can be illiquid and difficult to value, may involve leverage so that small changes produce disproportionate losses for the fund, and instruments not traded on an exchange are subject to the risk that a counterparty to the transaction will fail to meet its obligations under the derivatives contract. The fund’s principal use of derivatives involves the risk that anticipated interest rate movements and changes in currency values and currency exchange rates will not be accurately predicted, which could significantly harm the fund’s performance.

Risk Lose Money [Text]

rr_RiskLoseMoney

The fund’s share price fluctuates, which means you could lose money by investing in the fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-638-8790

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

troweprice.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The fund’s past performance (before and after taxes) is not necessarily an indication of future performance.

Bar Chart [Heading]

rr_BarChartHeading

Institutional Core Plus Fund
Calendar Year Returns

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

	*Quarter*	*Total*
	Ended	Return
Best Quarter	6/30/09	6.14%
Worst Quarter	9/30/08	-1.84%

The fund's return for the six months ended 6/30/12 was 3.48%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total ReturnsPeriods ended
December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

After-tax returns shown are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as a 401(k) account or individual retirement account.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available through troweprice.com or may be obtained by calling 1-800-638-8790.

Institutional Class | T. Rowe Price Institutional Core Plus Fund | T. Rowe Price Institutional Core Plus Fund

Acquired fund fees and expenses

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.40%

Other expenses

rr_OtherExpensesOverAssets

none

rr_AcquiredFundFeesAndExpensesOverAssets

0.06%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.46%

Fee waiver/expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.06%

^[1]

Total annual fund operating expenses after fee waiver/expense reimbursement

rr_NetExpensesOverAssets

0.40%

^[2]

1 year

rr_ExpenseExampleYear01

3 years

rr_ExpenseExampleYear03

128

5 years

rr_ExpenseExampleYear05

224

10 years

rr_ExpenseExampleYear10

505

2005

rr_AnnualReturn2005

2.90%

2006

rr_AnnualReturn2006

4.38%

2007

rr_AnnualReturn2007

6.38%

2008

rr_AnnualReturn2008

0.54%

2009

rr_AnnualReturn2009

14.53%

2010

rr_AnnualReturn2010

8.40%

2011

rr_AnnualReturn2011

6.23%

Year to Date Return, Label

rr_YearToDateReturnLabel

The fund's return for the six months ended 6/30/12

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Jun. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

3.48%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

6.14%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2008

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(1.84%)

rr_AverageAnnualReturnYear01

6.23%

rr_AverageAnnualReturnYear05

7.12%

rr_AverageAnnualReturnSinceInception

6.18%

rr_AverageAnnualReturnInceptionDate

Nov. 30, 2004

Institutional Class | T. Rowe Price Institutional Core Plus Fund | Returns after taxes on distributions | T. Rowe Price Institutional Core Plus Fund

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

4.46%

rr_AverageAnnualReturnYear05

5.18%

rr_AverageAnnualReturnSinceInception

4.57%

rr_AverageAnnualReturnInceptionDate

Nov. 30, 2004

Institutional Class | T. Rowe Price Institutional Core Plus Fund | Returns after taxes on distributions and sale of fund shares | T. Rowe Price Institutional Core Plus Fund

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

4.16%

rr_AverageAnnualReturnYear05

4.98%

rr_AverageAnnualReturnSinceInception

4.45%

rr_AverageAnnualReturnInceptionDate

Nov. 30, 2004

Institutional Class | T. Rowe Price Institutional Core Plus Fund | Barclays U.S. Aggregate Bond Index (reflects no deduction for fees, expenses, or taxes)

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

7.84%

rr_AverageAnnualReturnYear05

6.50%

rr_AverageAnnualReturnSinceInception

5.67%

Institutional Class | T. Rowe Price Institutional Core Plus Fund | Lipper Intermediate Investment Grade Debt Funds Average

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

6.22%

rr_AverageAnnualReturnYear05

5.57%

rr_AverageAnnualReturnSinceInception

4.87%

[1]

[2]

XML 18 R1.htm IDEA: XBRL DOCUMENT

Document and Entity Information	12 Months Ended
Document and Entity Information	Oct. 01, 2012
Risk/Return:
Document Type	485BPOS
Document Period End Date	May 31, 2012
Registrant Name	T. Rowe Price Institutional Income Funds, Inc.
Central Index Key	0001169187
Amendment Flag	false
Document Creation Date	Sep. 27, 2012
Document Effective Date	Oct. 01, 2012
Prospectus Date	Oct. 01, 2012

XML 19 R13.htm IDEA: XBRL DOCUMENT

Label

Element

Value

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

T. Rowe Price Institutional Income Funds, Inc.

Prospectus Date

rr_ProspectusDate

Oct. 01, 2012

F Class | T. Rowe Price Institutional Core Plus Fund

Objective, Primary [Text Block]

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

T. Rowe Price

Institutional Core Plus Fund–F Class

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

rr_ObjectivePrimaryTextBlock

The fund seeks to maximize total return through income and capital appreciation.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses

Expense Narrative [Text Block]

rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the fund.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Fees and Expenses of the Fund’s F Class

Annual fund operating expenses
(expenses that you pay each year as a
percentage of the value of your investment)

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover [Text Block]

rr_PortfolioTurnoverTextBlock

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

140.60%

Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]

rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

Strategy [Heading]

rr_StrategyHeading

Investments, Risks, and Performance

Principal Investment Strategies

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

Risk [Heading]

rr_RiskHeading

Principal Risks

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

As with any mutual fund, there is no guarantee that the fund will achieve its objective. The fund’s share price fluctuates, which means you could lose money by investing in the fund. The principal risks of investing in this fund are summarized as follows:

Active management risk The fund is subject to the risk that the investment adviser’s judgments about the attractiveness, value, or potential appreciation of the fund’s investments may prove to be incorrect. If the securities selected and strategies employed by the fund fail to produce the intended results, the fund could underperform other funds with similar objectives and investment strategies.

Interest rate risk This is the risk that a rise in interest rates will cause the price of a fixed rate debt security to fall. Generally, securities with longer maturities and funds with longer weighted average maturities carry greater interest rate risk.

Credit risk This is the risk that an issuer of a debt security could suffer an adverse change in financial condition that results in a payment default, security downgrade, or inability to meet a financial obligation. The fund’s exposure to credit risk is increased to the extent the fund invests in noninvestment-grade “junk” bonds. Junk bonds should be considered speculative as they carry greater risk of default and erratic price swings due to adverse changes in the credit quality of the issuer.

Liquidity risk This is the risk that the fund may not be able to sell a holding in a timely manner at a desired price.

Foreign investing risk This is the risk that the fund’s investments in foreign securities may be adversely affected by political and economic conditions overseas, reduced liquidity, or decreases in foreign currency values relative to the U.S. dollar. These risks are heightened for the fund’s investments in emerging markets. Any attempts at hedging currencies may not be successful and could cause the fund to lose money.

Prepayment risk and extension risk Prepayment risk is the risk that the principal on mortgage-backed securities, other asset-backed securities or any debt security with an embedded call option may be prepaid at any time, which could reduce yield and market value. The rate of prepayments tends to increase as interest rates fall, which could cause the average maturity of the portfolio to shorten. Extension risk may result from a rise in interest rates, which tends to make mortgage-backed securities, asset-backed securities, and other callable debt securities more volatile.

Derivatives risk To the extent the fund uses interest rate futures and forward currency exchange contracts, it is exposed to additional volatility in comparison to investing directly in bonds and other debt securities. These instruments can be illiquid and difficult to value, may involve leverage so that small changes produce disproportionate losses for the fund, and instruments not traded on an exchange are subject to the risk that a counterparty to the transaction will fail to meet its obligations under the derivatives contract. The fund’s principal use of derivatives involves the risk that anticipated interest rate movements and changes in currency values and currency exchange rates will not be accurately predicted, which could significantly harm the fund’s performance.

Risk Lose Money [Text]

rr_RiskLoseMoney

The fund’s share price fluctuates, which means you could lose money by investing in the fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

1-800-638-8790

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

troweprice.com

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

The fund’s past performance (before and after taxes) is not necessarily an indication of future performance.

Bar Chart [Heading]

rr_BarChartHeading

Institutional Core Plus Fund–F Class
Calendar Year Returns

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

	*Quarter*	*Total*
	Ended	Return
Best Quarter	12/31/11	2.00%
Worst Quarter	3/31/11	0.73%

The fund's return for the six months ended 6/30/12 was 3.42%.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total ReturnsPeriods ended
December 31, 2011

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

After-tax returns shown are not relevant to investors who hold their fund shares through tax-deferred arrangements, such as a 401(k) account or individual retirement account.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

Performance Table Closing [Text Block]

rr_PerformanceTableClosingTextBlock

Updated performance information is available through troweprice.com or may be obtained by calling 1-800-638-8790.

F Class | T. Rowe Price Institutional Core Plus Fund | T. Rowe Price Institutional Core Plus Fund-F Class

Acquired fund fees and expenses

rr_RiskReturnAbstract

Management fee

rr_ManagementFeesOverAssets

0.40%

Other expenses

rr_OtherExpensesOverAssets

0.10%

rr_AcquiredFundFeesAndExpensesOverAssets

0.06%

Total annual fund operating expenses

rr_ExpensesOverAssets

0.56%

Fee waiver/expense reimbursement

rr_FeeWaiverOrReimbursementOverAssets

0.06%

^[1]

Total annual fund operating expenses after fee waiver/expense reimbursement

rr_NetExpensesOverAssets

0.50%

^[2]

1 year

rr_ExpenseExampleYear01

3 years

rr_ExpenseExampleYear03

160

5 years

rr_ExpenseExampleYear05

280

10 years

rr_ExpenseExampleYear10

628

2011

rr_AnnualReturn2011

6.20%

Year to Date Return, Label

rr_YearToDateReturnLabel

The fund's return for the six months ended 6/30/12

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Jun. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

3.42%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Best Quarter

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Dec. 31, 2011

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

2.00%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Worst Quarter

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Mar. 31, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

0.73%

rr_AverageAnnualReturnYear01

6.20%

rr_AverageAnnualReturnSinceInception

4.44%

rr_AverageAnnualReturnInceptionDate

Sep. 28, 2010

F Class | T. Rowe Price Institutional Core Plus Fund | Returns after taxes on distributions | T. Rowe Price Institutional Core Plus Fund-F Class

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

4.44%

rr_AverageAnnualReturnSinceInception

2.42%

rr_AverageAnnualReturnInceptionDate

Sep. 28, 2010

F Class | T. Rowe Price Institutional Core Plus Fund | Returns after taxes on distributions and sale of fund shares | T. Rowe Price Institutional Core Plus Fund-F Class

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

4.14%

rr_AverageAnnualReturnSinceInception

2.74%

rr_AverageAnnualReturnInceptionDate

Sep. 28, 2010

F Class | T. Rowe Price Institutional Core Plus Fund | Barclays U.S. Aggregate Bond Index (reflects no deduction for fees, expenses, or taxes)

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

7.84%

rr_AverageAnnualReturnSinceInception

4.99%

F Class | T. Rowe Price Institutional Core Plus Fund | Lipper Intermediate Investment Grade Debt Funds Average

rr_RiskReturnAbstract

rr_AverageAnnualReturnYear01

6.22%