<Page>
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
FORM 11-K
ANNUAL REPORT PURSUANT TO SECTION 15(d) OF
THE SECURITIES EXCHANGE ACT OF 1934
For the fiscal year ended December 31, 2000
Commission file number 1-3004
Illinois Power Company
Incentive Savings Plan
(Full title of the plan)
Dynegy Inc.
1000 Louisiana
Suite 5800
Houston, Texas 77002
(Name of issuer of the securities held
pursuant to the plan and the address
of its principal executive office.)
<Page>
ILLINOIS POWER COMPANY
INCENTIVE SAVINGS PLAN
INDEX TO FINANCIAL STATEMENTS AND ADDITIONAL INFORMATION
DECEMBER 31, 2000 AND 1999
--------------------------------------------------------------------------------
PAGE
Financial Statements:
Report of Independent Accountants 1
Statement of Net Assets Available for Benefits
as of December 31, 2000 and 1999 2
Statement of Changes in Net Assets Available for
Benefits for the years ended December 31, 2000 and 1999 3
Notes to Financial Statements 4-11
Additional Information:
Schedule of Assets (Held at End of Year)
December 31, 2000 Schedule I
Note: Other schedules required by 29 CFR 2520.103-10 of the Department of
Labor's Rules and Regulations for reporting and disclosure under ERISA
have been omitted because they are not applicable.
<Page>
REPORT OF INDEPENDENT ACCOUNTANTS
To the Participants and Administrator of
The Illinois Power Company
Incentive Savings Plan
In our opinion, the accompanying statement of net assets available for benefits
and the related statement of changes in net assets available for benefits
present fairly, in all material respects, the net assets available for benefits
of the Illinois Power Company Incentive Savings Plan (the "Plan") at December
31, 2000 and 1999, and the changes in net assets available for benefits for the
years then ended in conformity with accounting principles generally accepted in
the United States of America. These financial statements are the responsibility
of the Plan's management; our responsibility is to express an opinion on these
financial statements based on our audits. We conducted our audits of these
statements in accordance with auditing standards generally accepted in the
United States of America, which require that we plan and perform the audit to
obtain reasonable assurance about whether the financial statements are free of
material misstatement. An audit includes examining, on a test basis, evidence
supporting the amounts and disclosures in the financial statements, assessing
the accounting principles used and significant estimates made by management, and
evaluating the overall financial statement presentation. We believe that our
audits provide a reasonable basis for our opinion.
As explained in Note 1 to the financial statements, Illinois Power Company sold
its Clinton Nuclear Power Plant ("Clinton") to AmerGen Energy Company
("AmerGen") on December 15, 1999. Under terms of the sales agreement, Plan
account balances relating to Clinton employees were transferred to AmerGen on
January 21, 2000.
Our audits were conducted for the purpose of forming an opinion on the basic
financial statements taken as a whole. The supplemental Schedule of Assets (Held
at End of Year) is presented for the purpose of additional analysis and is not a
required part of the basic financial statements but is supplementary information
required by the Department of Labor's Rules and Regulations for Reporting and
Disclosure under the Employee Retirement Income Security Act of 1974. This
supplemental schedule is the responsibility of the Plan's management. The
supplemental schedule has been subjected to the auditing procedures applied in
the audits of the basic financial statements and, in our opinion, is fairly
stated in all material respects in relation to the basic financial statements
taken as a whole.
PricewaterhouseCoopers LLP
September 28, 2001
<Page>
ILLINOIS POWER COMPANY
INCENTIVE SAVINGS PLAN
STATEMENT OF NET ASSETS AVAILABLE FOR BENEFITS
DECEMBER 31, 2000 AND 1999
--------------------------------------------------------------------------------
<Table>
<Caption>
DECEMBER 31,
2000 1999
Assets:
Cash and temporary cash investments $ 605,881 $ 778,291
Investments at fair value 211,108,751 226,773,748
Participant loans 2,357,978 4,133,430
------------- -------------
Total investments 214,072,610 231,685,469
------------- -------------
Dividends and interest receivable 3,374 1,596
Employee contributions receivable - 259,160
Employer contributions receivable 697,911 3,343,289
------------- -------------
701,285 3,604,045
------------- -------------
Total assets 214,773,895 235,289,514
------------- -------------
Liabilities:
Transfer to AmerGen (Note 1) - 61,210,672
------------- -------------
Total liabilities - 61,210,672
------------- -------------
Net assets available for benefits $ 214,773,895 $ 174,078,842
============= =============
</Table>
The accompanying notes are an integral part of these financial statements.
-2-
<Page>
ILLINOIS POWER COMPANY
INCENTIVE SAVINGS PLAN
STATEMENT OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS
FOR THE YEARS ENDED DECEMBER 31, 2000 AND 1999
--------------------------------------------------------------------------------
<Table>
<Caption>
YEAR ENDED
DECEMBER 31,
2000 1999
Sources of participants' equity:
Contributions:
Employee $ 5,317,696 $ 9,573,968
Employer 1,550,540 5,841,996
------------- --------------
6,868,236 15,415,964
------------- --------------
Investment income:
Dividend and interest income 15,541,453 19,248,968
Net appreciation in fair value of investments 52,248,264 30,137,923
------------- --------------
67,789,717 49,386,891
------------- --------------
Application of participants' equity:
Distributions to active and terminated participants 31,035,763 8,380,075
Administrative and miscellaneous expenses 13,847 41,294
------------- --------------
31,049,610 8,421,369
------------- --------------
Increase in net assets available for benefits 43,608,343 56,381,486
Transfer to AmerGen (Note 1) (2,913,290) (61,210,672)
Plan-to-plan transfers - 626,204
Net assets available for benefits:
Beginning of year 174,078,842 178,281,824
------------- --------------
End of year $ 214,773,895 $ 174,078,842
============= ==============
</Table>
The accompanying notes are an integral part of these financial statements.
-3-
<Page>
ILLINOIS POWER COMPANY
INCENTIVE SAVINGS PLAN
NOTES TO FINANCIAL STATEMENTS
DECEMBER 31, 2000 AND 1999
--------------------------------------------------------------------------------
1. DESCRIPTION OF THE PLAN
GENERAL
The Illinois Power Company Incentive Savings Plan (the Plan) is
sponsored and administered by Illinois Power Company (the Company or
Plan Administrator). The Plan became effective as of June 1, 1984.
Assets of the Plan are held and managed by a trustee. Effective July
1, 1995, Fidelity Management Trust Company of Boston, Massachusetts
became trustee and custodian. The purpose of the Plan is to enable
participants to invest a portion of their salaries in tax-deferred
savings pursuant to section 401(k) of the Internal Revenue Code
(IRC). The Plan is subject to and in compliance with the provisions
of the Employee Retirement Income Security Act of 1974 (ERISA) as
amended. On February 1, 2000 Illinova Corporation, the parent company,
merged with Dynegy Inc. No significant changes have yet been made to
the Plan as a result of the merger, except for the one-for-one
conversion of Illinova common stock into Dynegy common stock on the
effective date of the merger.
PARTICIPATION
All salaried employees of the Company are eligible to participate in
the Plan. Participation is voluntary. Active participation ceases upon
termination of employment with the Company. Former employees can choose
to liquidate their accounts or to leave them in the Plan. Earnings will
continues to accrue on undistributed accounts. All accounts, whether
for active or former employees, are fully vested.
PLAN CHANGES AND AMENDMENTS
Effective January 1, 1999, the Company match contribution was
increased. The Company had previously matched 50% of the first $80 of
the participants' monthly before tax contributions and 25% of the
balance of the contributions for the month, up to 6% of the employee's
base earnings for the month. Effective January 1, 1999, the Company
began matching 50% of the participants' monthly before tax
contributions, up to 6% of the employee's base earnings for the month.
Effective December 15, 1999, Illinois Power sold its Clinton Nuclear
Power Plant to AmerGen Energy Company (AmerGen). Under terms of the
sales agreement, Plan account balances of $61,210,672 relating to
Clinton employees were transferred to AmerGen on January 21, 2000.
Such amounts were reflected as liabilities of the Plan at December
31, 1999 in the Statement of Net Assets Available for Benefits. An
additional $2,913,290 related primarily to incentive compensation
contributions and participant loans was later transferred to AmerGen
during 2000 and is reflected as a decrease to net assets available
for benefits in the Statement of Changes in Net Assets Available for
Benefits for the year ended December 31, 2000.
AmerGen's plan would not accept transfer of the Fidelity Brokerage
Link. Employees who participated in this option were asked to liquidate
their accounts and transfer the funds to other funds or to the Fidelity
Retirement Money Market Fund. The trustee liquidated the accounts of
employees who did not comply with the request, and transferred the
proceeds to the Fidelity Retirement Money Market Fund. This fund is not
ordinarily an available option for contributions; it was used only to
facilitate the liquidation of the Brokerage Link accounts. At December
31, 2000 and 1999, the fund held $46 and $2,045,746, respectively.
-4-
<Page>
ILLINOIS POWER COMPANY
INCENTIVE SAVINGS PLAN
NOTES TO FINANCIAL STATEMENTS
DECEMBER 31, 2000 AND 1999
--------------------------------------------------------------------------------
CONTRIBUTIONS
Participants may make before-tax contribution by payroll deduction up
to the legal dollar limit. Participants may also make after-tax
contributions in cash or by payroll deduction. Total contributions are
limited to the applicable percentage limit set by law. A participant
may also "roll-over" into the Plan amounts previously invested in
another retirement plan.
Participants have the option of investing their contributions into any
or all of the investment funds in the proportions they choose. They may
change their investment options or transfer amounts from fund to fund
at any time. Amounts are transferred to or from the Illinois Power
Company Incentive Savings Plan as participants' shift out of or into
positions covered by a collective bargaining agreement. These transfers
are shown in the Statement of Changes in Net Assets Available for
Benefits as plan-to-plan transfers.
The Company contributes a monthly match to the Plan equal to 50% of the
participants' monthly before-tax contributions, up to 6% of the
employee's base earnings for the month. All Company matching
contributions are made in units of Dynegy common stock and are
contained in the Stock Fund. Dividends on stock held in the Stock Fund
are also invested in the Stock Fund.
The Company has an Incentive Compensation arrangement in which all
participants employed by the Company on the last day of the Plan year
are eligible to earn Dynegy stock if specified performance goals are
met. Units awarded under the Incentive Compensation arrangement are
held in the Stock Fund. Dividends earned on these units are also
invested in the Stock Fund. See Note 5 for more information.
Shares previously held in the Tax Reduction Act Stock Ownership Plan
(TRASOP), which was eliminated in 1988, are also held in the Stock
Fund.
ESOP
In October 1990, the Board of Directors authorized amendments to the
Incentive Savings Plan to provide for the implementation of an Employee
Stock Ownership Plan (ESOP) arrangement. Under this arrangement, the
Company, pursuant to authorization granted by the Illinois Commerce
Commission (ICC), loaned $35 million to the Trustee of the ESOP in
January 1991. The loan proceeds were used to purchase 2,031,445 shares
of the Company's common stock on the open market. These shares are held
in a suspense account under the Plans and are being distributed to the
accounts of participating employees as the loan is repaid by the
Trustee with funds contributed by Illinois Power, together with
dividends on the shares acquired with the loan proceeds. The shares are
allocated to the accounts of eligible participating employees as they
are earned through the Match or Incentive Compensation features of the
Plan.
As of December 31, 2000 and 1999, 484,688 and 493,449 shares have been
allocated to salaried employees for Matching Contribution and Company
Incentive Contributions.
DISTRIBUTIONS
Distributions as provided for in the Plan are made to retired Plan
participants or their beneficiaries. Distributions must begin by April
1st of the calendar year following the later of the calendar year in
which the employee reaches age 70 1/2 or the calendar year in which the
employee retires. All distributions are made in the form of cash and/or
Dynegy common stock.
-5-
<Page>
ILLINOIS POWER COMPANY
INCENTIVE SAVINGS PLAN
NOTES TO FINANCIAL STATEMENTS
DECEMBER 31, 2000 AND 1999
--------------------------------------------------------------------------------
FORFEITURES
Each participant is responsible for supplying the Company with a
current address. If the address of the participant (or the
participant's beneficiary in the event of participant's death) is not
known to the Company within four years (three years in the event of
participant's death) of the date on which distribution may first be
made, the adjusted balance in the participant's account shall be deemed
a forfeiture and shall be used to reduce matching contributions and
company incentive contributions.
LOANS
The Plan allows participants to borrow from their before-tax accounts
an amount not to exceed the lessor of $50,000 reduced by the excess of
the highest outstanding balance of loans during the one-year before the
date the loan is made over the outstanding balance of loans on the date
the loan is made or 50% of the vested account balance. Interest is
charged on these loans at a rate commensurate with interest rates
charged by persons in the business of lending money for similar type
loans. For 2000, the interest rates ranged from 9.5% to 10.5%; for 1999
the rate ranged from 8.75% to 9.50%.
All loans made will mature and be payable in full no earlier than one
year and no later than five years from the date of the loan. An
exception exists when the loan is used by the participant to acquire
his or her principal residence. In this case, the loan will mature and
be payable in full no earlier than one year and no later than ten years
from the date of the loan. Loan repayments are made by payroll
deductions authorized by the participant and by optional cash payments.
Interest paid on the loan is credited to the participant's account. The
Trustee maintains a Loan Fund to hold the balances of participants'
loans.
PLAN TERMINATION
The right to amend, notify or terminate the Plan is reserved by the
Company provided that such action does not retroactively and adversely
affect the rights of any participant or beneficiary under the Plan.
2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES
BASIS OF ACCOUNTING
The accompanying Plan financial statements are prepared on the accrual
basis of accounting.
INVESTMENTS
Participant loans included in the loan fund are valued at cost, which
approximates fair value. Other investments are stated at current value
based on the latest quoted market price.
Investment securities are exposed to various risks, such as interest
rate, market, and credit. Due to the level of risk associated with
certain investment securities and the level of uncertainty related to
changes in the value of investment securities, it is at least
reasonably possible that changes in risks in the near term could
materially affect the amounts reported in the Statement of Net Assets
Available for Benefits.
-6-
<Page>
ILLINOIS POWER COMPANY
INCENTIVE SAVINGS PLAN
NOTES TO FINANCIAL STATEMENTS
DECEMBER 31, 2000 AND 1999
--------------------------------------------------------------------------------
INCOME
Interest and dividend income is recorded as earned.
Net appreciation (depreciation) of investments is comprised of realized
and unrealized gains and losses. Realized gains or losses represent the
difference between proceeds received upon sale and the average cost of
the investment. Unrealized gain or loss is the difference between
market value and cost of investments retained in the Plan (at financial
statement date). For the purpose of allocation to participants, the
Dynegy common stock is valued by the Plan at market value on the date
of allocation and current value is used at the time of distribution to
participants resulting in a realized gain or loss and is reflected in
the Net Appreciation in Fair Value of Investments in the Statement of
Changes in Net Assets Available for Benefits.
EXPENSES
Certain expenses incurred in the administration of the Plan are paid by
the Plan rather than the Company. The expenses paid by the Plan include
ESOP record keeping fees and trustee administrative fees. All other
expenses incurred in the operation of the Plan are paid by the Company.
INCOME TAXES
The Internal Revenue service has determined and informed the Company by
a letter dated January 8, 1996, that the Plan and related trust are
designed in accordance with applicable sections of the IRC. The Plan
has been amended since receiving the determination letter. However, the
Plan Administrator and the Plan's tax counsel believe that the Plan is
designed and is currently being operated in compliance with the
applicable requirements of the IRC.
USE OF ESTIMATES
The preparation of financial statements in conformity with generally
accepted accounting principles requires management to make estimates
and assumptions that affect the reported amounts of assets and
liabilities at the date of the financial statements and the reported
amounts of revenues and expenses during the reporting period. Actual
results could differ from these estimates.
DISTRIBUTION OF BENEFITS
Distributions of benefits are recorded when paid.
-7-
<Page>
ILLINOIS POWER COMPANY
INCENTIVE SAVINGS PLAN
NOTES TO FINANCIAL STATEMENTS
DECEMBER 31, 2000 AND 1999
--------------------------------------------------------------------------------
3. INVESTMENTS
Plan investments are received, invested and held by the Trustee.
Individual investments that represent 5% or more of the Plan's net
assets available for benefits include:
DECEMBER 31,
INVESTMENTS AT FAIR VALUE AS 2000
DETERMINED BY QUOTED MARKET PRICE FAIR VALUE
Dynegy Common Stock $ 90,131,849
Fidelity Equity Income Fund $ 25,722,445
Fidelity Independence Fund* $ 46,737,212
Fidelity Managed Income Portfolio $ 16,665,376
* Formerly Fidelity Retirement Growth Fund
DECEMBER 31,
INVESTMENTS AT FAIR VALUE AS 1999
DETERMINED BY QUOTED MARKET PRICE FAIR VALUE
Illinova Common Stock $ 36,336,720
Fidelity Equity Income Fund $ 40,325,424
Fidelity Retirement Growth Fund $ 69,023,023
Fidelity Managed Income Portfolio $ 21,765,711
Fidelity U.S. Equity Index Pooled Fund $ 12,091,053
4. TRANSACTIONS WITH PARTIES-IN-INTEREST
Certain Plan investments are shares of mutual funds managed by Fidelity
Management Trust Company. Fidelity Management Trust Company is the
trustee as defined by the Plan and, therefore, these transactions
qualify as party-in-interest. Fees paid during the year for legal,
accounting, actuarial and other professional services rendered by
parties-in-interest were based on customary and reasonable rates for
such services.
-8-
<Page>
ILLINOIS POWER COMPANY
INCENTIVE SAVINGS PLAN
NOTES TO FINANCIAL STATEMENTS
DECEMBER 31, 2000 AND 1999
--------------------------------------------------------------------------------
5. NONPARTICIPANT-DIRECTED INVESTMENTS
All funds in the Plan are participant directed, with the exception of
the Stock Fund, which is partially nonparticipant directed as pertains
to the Company match and incentive compensation features of the Plan.
Information about the net assets and the significant components of the
changes in net assets relating to the Stock Fund is as follows:
<Table>
<Caption>
DECEMBER 31,
2000 1999
Assets:
Cash and temporary cash investments $ 244,629 $ 339,276
Investments at fair value 90,131,849 36,336,720
------------ ------------
Total investments 90,376,478 36,675,996
Dividends and interest receivable 3,374 1,596
Employee contributions receivable - 4,966
Employer contributions receivable 697,911 3,343,289
------------ ------------
Other assets 701,285 3,349,851
------------ ------------
Total assets 91,077,763 40,025,847
------------ ------------
Liabilities:
Assets transferred to AmerGen - 10,244,086
------------ ------------
Total liabilities - 10,244,086
------------ ------------
Net assets available for benefits $ 91,077,763 $ 29,781,761
============ ============
</Table>
-9-
<Page>
ILLINOIS POWER COMPANY
INCENTIVE SAVINGS PLAN
NOTES TO FINANCIAL STATEMENTS
DECEMBER 31, 2000 AND 1999
--------------------------------------------------------------------------------
<Table>
<Caption>
DECEMBER 31,
2000 1999
Sources of participants' equity:
Contributions:
Employee $ 239,172 $ 149,468
Employer 1,550,540 5,841,996
------------ ------------
1,789,712 5,991,464
------------ ------------
Investment income:
Dividend and interest income 963,297 1,332,489
Net change in fair value of investments 66,537,766 10,479,096
------------ ------------
67,501,063 11,811,585
------------ ------------
Application of participants' equity:
Distributions to active and terminated participants 6,949,848 1,385,479
Administrative and miscellaneous expenses 1,395 24,263
------------ ------------
6,951,243 1,409,742
Increase (decrease) in net assets available for benefits
prior to transfers 62,339,532 16,393,307
Plan-to-plan transfers - 197,561
Loans to participants, net (46,748) 694
Fund-to-fund transfers 348,637 (2,701,036)
Assets transferred to AmerGen (1,345,419) (10,244,086)
Net assets available for benefits:
Beginning of year 29,781,761 26,135,321
------------ ------------
End of year $ 91,077,763 $ 29,781,761
============ ============
</Table>
-10-
<Page>
ILLINOIS POWER COMPANY
INCENTIVE SAVINGS PLAN
NOTES TO FINANCIAL STATEMENTS
DECEMBER 31, 2000 AND 1999
--------------------------------------------------------------------------------
6. RECONCILIATION OF FINANCIAL STATEMENTS TO FORM 5500
<Table>
<Caption>
The following is a reconciliation of net assets available for
benefits per the financial statements to Form 5500:
DECEMBER 31,
2000 1999
Net assets available for benefits per the
financial statements $ 214,773,895 $ 174,078,842
Accrued distributions of benefits 20,793 -
------------- -------------
Net assets available for benefits per the Form 5500 $ 214,753,102 $ 174,078,842
============= =============
</Table>
The following is a reconciliation of benefits distributed to
participants per the financial statements to the Form 5500:
<Table>
<Caption>
YEAR ENDED
DECEMBER 31,
2000
Distribution of benefits per the financial statements $ 31,035,763
Add: accrued distribution of benefits at December 31, 2000 20,793
Less: accrued distribution of benefits at December 31, 1999 -
------------
Distribution of benefits per the Form 5500 $ 31,056,556
============
</Table>
-11-
<Page>
ILLINOIS POWER COMPANY SCHEDULE I
INCENTIVE SAVINGS PLAN
SCHEDULE OF ASSETS (HELD AT END OF YEAR)
DECEMBER 31, 2000
--------------------------------------------------------------------------------
<Table>
<Caption>
IDENTITY OF ISSUE/ FAIR
DESCRIPTION OF INVESTMENT COST VALUE
*Dynegy Common Stock $ 22,974,361 $ 90,131,849
*Fidelity Equity Income Fund 19,908,260 25,722,445
*Fidelity Independence Fund 43,295,507 46,737,212
*Fidelity Asset Manager Income Fund 1,163,430 1,143,900
*Fidelity Asset Manager Growth Fund 5,043,039 4,677,772
*Fidelity Asset Manager Fund 7,184,006 7,222,295
*Fidelity International Growth and Income Fund 3,300,332 3,353,430
*Fidelity Managed Income Portfolio Fund 16,665,376 16,665,376
*Fidelity US Equity Index Commingled Pool 4,499,231 5,239,149
*Founders Growth Fund 5,749,050 4,061,630
*USAA International Fund 603,844 564,756
*Warburg Pincus Emerging Growth 2,784,627 2,198,513
*Fidelity Brokerage Link 3,751,093 3,390,378
*Fidelity Retirement Money Market Fund 46 46
*Participant Loans** 2,357,978 2,357,978
------------- --------------
$ 139,280,180 $ 213,466,729
============= ==============
</Table>
*A party-in-interest to the plan
**Interest rates on loans range from 9.5% to 10.5%
<Page>
SIGNATURE
Pursuant to the requirements of the Securities Exchange Act of 1934, Illinois
Power Company had duly caused this annual report to be signed on its behalf by
the undersigned hereunto duly authorized.
Illinois Power Company
Incentive Savings Plan
By: /s/ Ron Oliver
------------------------------------------
Ron Oliver
Human Resources Transition Manager
Date: October 17, 2001
<Page>
EXHIBIT INDEX
EXHIBITS FILED HEREWITH
--------------------------------------------------------------------------------
Exhibit No. Description
--------------------------------------------------------------------------------
1 Consent of Independent Accountants