<Page>

                                                                      EXHIBIT 24

                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that the person whose signature
appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran,
Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to
act without the others, his true and lawful attorneys-in-fact and agents, with
full and several power of substitution and resubstitution for the undersigned
and in the undersigned's name, place and stead, in any and all capacities, to
sign a registration statement (the "Registration Statement") under the
Securities Act of 1933, as amended, for the registration of up to $250,000,000
aggregate principal amount of 6.20% Notes due 2007 and any and all amendments
and supplements thereto or to the prospectus contained therein, (including
pre-effective and post-effective amendments) to such Registration Statement, and
to file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any and all
documents relating to the qualification or registration under state Blue Sky or
securities laws of such securities, granting unto such attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as the undersigned might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents or any of them, or their or his substitute or substitutes, may lawfully
do or cause to be done by virtue hereof.

                 IN WITNESS WHEREOF, the undersigned has signed his/her name
effective as of July 19, 2002.

                                                 /s/ Edgar D. Jannotta
                                                 -------------------------------

<Page>

                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that the person whose signature
appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran,
Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to
act without the others, his true and lawful attorneys-in-fact and agents, with
full and several power of substitution and resubstitution for the undersigned
and in the undersigned's name, place and stead, in any and all capacities, to
sign a registration statement (the "Registration Statement") under the
Securities Act of 1933, as amended, for the registration of up to $250,000,000
aggregate principal amount of 6.20% Notes due 2007 and any and all amendments
and supplements thereto or to the prospectus contained therein, (including
pre-effective and post-effective amendments) to such Registration Statement, and
to file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any and all
documents relating to the qualification or registration under state Blue Sky or
securities laws of such securities, granting unto such attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as the undersigned might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents or any of them, or their or his substitute or substitutes, may lawfully
do or cause to be done by virtue hereof.

                 IN WITNESS WHEREOF, the undersigned has signed his/her name
effective as of July 19, 2002.

                                                 /s/ Lester B. Knight
                                                 -------------------------------

<Page>

                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that the person whose signature
appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran,
Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to
act without the others, his true and lawful attorneys-in-fact and agents, with
full and several power of substitution and resubstitution for the undersigned
and in the undersigned's name, place and stead, in any and all capacities, to
sign a registration statement (the "Registration Statement") under the
Securities Act of 1933, as amended, for the registration of up to $250,000,000
aggregate principal amount of 6.20% Notes due 2007 and any and all amendments
and supplements thereto or to the prospectus contained therein, (including
pre-effective and post-effective amendments) to such Registration Statement, and
to file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any and all
documents relating to the qualification or registration under state Blue Sky or
securities laws of such securities, granting unto such attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as the undersigned might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents or any of them, or their or his substitute or substitutes, may lawfully
do or cause to be done by virtue hereof.

                 IN WITNESS WHEREOF, the undersigned has signed his/her name
effective as of July 19, 2002.

                                                 /s/ Perry J. Lewis
                                                 -------------------------------

<Page>

                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that the person whose signature
appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran,
Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to
act without the others, his true and lawful attorneys-in-fact and agents, with
full and several power of substitution and resubstitution for the undersigned
and in the undersigned's name, place and stead, in any and all capacities, to
sign a registration statement (the "Registration Statement") under the
Securities Act of 1933, as amended, for the registration of up to $250,000,000
aggregate principal amount of 6.20% Notes due 2007 and any and all amendments
and supplements thereto or to the prospectus contained therein, (including
pre-effective and post-effective amendments) to such Registration Statement, and
to file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any and all
documents relating to the qualification or registration under state Blue Sky or
securities laws of such securities, granting unto such attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as the undersigned might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents or any of them, or their or his substitute or substitutes, may lawfully
do or cause to be done by virtue hereof.

                 IN WITNESS WHEREOF, the undersigned has signed his/her name
effective as of July 19, 2002.

                                                 /s/ R. Eden Martin
                                                 -------------------------------

<Page>

                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that the person whose signature
appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran,
Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to
act without the others, his true and lawful attorneys-in-fact and agents, with
full and several power of substitution and resubstitution for the undersigned
and in the undersigned's name, place and stead, in any and all capacities, to
sign a registration statement (the "Registration Statement") under the
Securities Act of 1933, as amended, for the registration of up to $250,000,000
aggregate principal amount of 6.20% Notes due 2007 and any and all amendments
and supplements thereto or to the prospectus contained therein, (including
pre-effective and post-effective amendments) to such Registration Statement, and
to file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any and all
documents relating to the qualification or registration under state Blue Sky or
securities laws of such securities, granting unto such attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as the undersigned might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents or any of them, or their or his substitute or substitutes, may lawfully
do or cause to be done by virtue hereof.

                 IN WITNESS WHEREOF, the undersigned has signed his/her name
effective as of July 19, 2002.

                                                 /s/ Andrew J. McKenna
                                                 -------------------------------

<Page>

                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that the person whose signature
appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran,
Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to
act without the others, his true and lawful attorneys-in-fact and agents, with
full and several power of substitution and resubstitution for the undersigned
and in the undersigned's name, place and stead, in any and all capacities, to
sign a registration statement (the "Registration Statement") under the
Securities Act of 1933, as amended, for the registration of up to $250,000,000
aggregate principal amount of 6.20% Notes due 2007 and any and all amendments
and supplements thereto or to the prospectus contained therein, (including
pre-effective and post-effective amendments) to such Registration Statement, and
to file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any and all
documents relating to the qualification or registration under state Blue Sky or
securities laws of such securities, granting unto such attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as the undersigned might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents or any of them, or their or his substitute or substitutes, may lawfully
do or cause to be done by virtue hereof.

                 IN WITNESS WHEREOF, the undersigned has signed his/her name
effective as of July 19, 2002.

                                                 /s/ Robert S. Morrison
                                                 -------------------------------

<Page>

                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that the person whose signature
appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran,
Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to
act without the others, his true and lawful attorneys-in-fact and agents, with
full and several power of substitution and resubstitution for the undersigned
and in the undersigned's name, place and stead, in any and all capacities, to
sign a registration statement (the "Registration Statement") under the
Securities Act of 1933, as amended, for the registration of up to $250,000,000
aggregate principal amount of 6.20% Notes due 2007 and any and all amendments
and supplements thereto or to the prospectus contained therein, (including
pre-effective and post-effective amendments) to such Registration Statement, and
to file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any and all
documents relating to the qualification or registration under state Blue Sky or
securities laws of such securities, granting unto such attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as the undersigned might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents or any of them, or their or his substitute or substitutes, may lawfully
do or cause to be done by virtue hereof.

                 IN WITNESS WHEREOF, the undersigned has signed his/her name
effective as of July 19, 2002.

                                                 /s/ Richard C. Notebaert
                                                 -------------------------------

<Page>

                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that the person whose signature
appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran,
Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to
act without the others, his true and lawful attorneys-in-fact and agents, with
full and several power of substitution and resubstitution for the undersigned
and in the undersigned's name, place and stead, in any and all capacities, to
sign a registration statement (the "Registration Statement") under the
Securities Act of 1933, as amended, for the registration of up to $250,000,000
aggregate principal amount of 6.20% Notes due 2007 and any and all amendments
and supplements thereto or to the prospectus contained therein, (including
pre-effective and post-effective amendments) to such Registration Statement, and
to file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any and all
documents relating to the qualification or registration under state Blue Sky or
securities laws of such securities, granting unto such attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as the undersigned might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents or any of them, or their or his substitute or substitutes, may lawfully
do or cause to be done by virtue hereof.

                 IN WITNESS WHEREOF, the undersigned has signed his/her name
effective as of July 19, 2002.

                                                 /s/ Michael D. O'Halleran
                                                 -------------------------------

<Page>

                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that the person whose signature
appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran,
Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to
act without the others, his true and lawful attorneys-in-fact and agents, with
full and several power of substitution and resubstitution for the undersigned
and in the undersigned's name, place and stead, in any and all capacities, to
sign a registration statement (the "Registration Statement") under the
Securities Act of 1933, as amended, for the registration of up to $250,000,000
aggregate principal amount of 6.20% Notes due 2007 and any and all amendments
and supplements thereto or to the prospectus contained therein, (including
pre-effective and post-effective amendments) to such Registration Statement, and
to file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any and all
documents relating to the qualification or registration under state Blue Sky or
securities laws of such securities, granting unto such attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as the undersigned might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents or any of them, or their or his substitute or substitutes, may lawfully
do or cause to be done by virtue hereof.

                 IN WITNESS WHEREOF, the undersigned has signed his/her name
effective as of July 19, 2002.

                                                 /s/ John W. Rogers, Jr.
                                                 -------------------------------

<Page>

                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that the person whose signature
appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran,
Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to
act without the others, his true and lawful attorneys-in-fact and agents, with
full and several power of substitution and resubstitution for the undersigned
and in the undersigned's name, place and stead, in any and all capacities, to
sign a registration statement (the "Registration Statement") under the
Securities Act of 1933, as amended, for the registration of up to $250,000,000
aggregate principal amount of 6.20% Notes due 2007 and any and all amendments
and supplements thereto or to the prospectus contained therein, (including
pre-effective and post-effective amendments) to such Registration Statement, and
to file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any and all
documents relating to the qualification or registration under state Blue Sky or
securities laws of such securities, granting unto such attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as the undersigned might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents or any of them, or their or his substitute or substitutes, may lawfully
do or cause to be done by virtue hereof.

                 IN WITNESS WHEREOF, the undersigned has signed his/her name
effective as of July 19, 2002.

                                                 /s/ Patrick G. Ryan, Jr.
                                                 -------------------------------

<Page>

                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that the person whose signature
appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran,
Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to
act without the others, his true and lawful attorneys-in-fact and agents, with
full and several power of substitution and resubstitution for the undersigned
and in the undersigned's name, place and stead, in any and all capacities, to
sign a registration statement (the "Registration Statement") under the
Securities Act of 1933, as amended, for the registration of up to $250,000,000
aggregate principal amount of 6.20% Notes due 2007 and any and all amendments
and supplements thereto or to the prospectus contained therein, (including
pre-effective and post-effective amendments) to such Registration Statement, and
to file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any and all
documents relating to the qualification or registration under state Blue Sky or
securities laws of such securities, granting unto such attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as the undersigned might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents or any of them, or their or his substitute or substitutes, may lawfully
do or cause to be done by virtue hereof.

                 IN WITNESS WHEREOF, the undersigned has signed his/her name
effective as of July 19, 2002.

                                                 /s/ George A. Schaefer
                                                 -------------------------------

<Page>

                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that the person whose signature
appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran,
Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to
act without the others, his true and lawful attorneys-in-fact and agents, with
full and several power of substitution and resubstitution for the undersigned
and in the undersigned's name, place and stead, in any and all capacities, to
sign a registration statement (the "Registration Statement") under the
Securities Act of 1933, as amended, for the registration of up to $250,000,000
aggregate principal amount of 6.20% Notes due 2007 and any and all amendments
and supplements thereto or to the prospectus contained therein, (including
pre-effective and post-effective amendments) to such Registration Statement, and
to file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any and all
documents relating to the qualification or registration under state Blue Sky or
securities laws of such securities, granting unto such attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as the undersigned might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents or any of them, or their or his substitute or substitutes, may lawfully
do or cause to be done by virtue hereof.

                 IN WITNESS WHEREOF, the undersigned has signed his/her name
effective as of July 19, 2002.

                                                 /s/ Carolyn Y. Woo
                                                 -------------------------------

<Page>

                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that the person whose signature
appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran,
Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to
act without the others, his true and lawful attorneys-in-fact and agents, with
full and several power of substitution and resubstitution for the undersigned
and in the undersigned's name, place and stead, in any and all capacities, to
sign a registration statement (the "Registration Statement") under the
Securities Act of 1933, as amended, for the registration of up to $250,000,000
aggregate principal amount of 6.20% Notes due 2007 and any and all amendments
and supplements thereto or to the prospectus contained therein, (including
pre-effective and post-effective amendments) to such Registration Statement, and
to file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any and all
documents relating to the qualification or registration under state Blue Sky or
securities laws of such securities, granting unto such attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as the undersigned might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents or any of them, or their or his substitute or substitutes, may lawfully
do or cause to be done by virtue hereof.

                 IN WITNESS WHEREOF, the undersigned has signed his/her name
effective as of July 19, 2002.

                                                 /s/ Patrick G. Ryan
                                                 -------------------------------

<Page>

                                POWER OF ATTORNEY

                 KNOW ALL MEN BY THESE PRESENTS, that the person whose signature
appears below constitutes and appoints Patrick G. Ryan, Michael D. O'Halleran,
Harvey N. Medvin and Raymond I. Skilling, and each of them, with full power to
act without the others, his true and lawful attorneys-in-fact and agents, with
full and several power of substitution and resubstitution for the undersigned
and in the undersigned's name, place and stead, in any and all capacities, to
sign a registration statement (the "Registration Statement") under the
Securities Act of 1933, as amended, for the registration of up to $250,000,000
aggregate principal amount of 6.20% Notes due 2007 and any and all amendments
and supplements thereto or to the prospectus contained therein, (including
pre-effective and post-effective amendments) to such Registration Statement, and
to file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, and any and all
documents relating to the qualification or registration under state Blue Sky or
securities laws of such securities, granting unto such attorneys-in-fact and
agents, and each of them, full power and authority to do and perform each and
every act and thing requisite or necessary to be done in and about the premises,
as fully to all intents and purposes as the undersigned might or could do in
person, hereby ratifying and confirming all that said attorneys-in-fact and
agents or any of them, or their or his substitute or substitutes, may lawfully
do or cause to be done by virtue hereof.

                 IN WITNESS WHEREOF, the undersigned has signed his/her name
effective as of July 19, 2002.

                                                 /s/ Harvey N. Medvin
                                                 -------------------------------