<PAGE>   1
                                                                      EXHIBIT 12

                       RATIO OF EARNINGS TO FIXED CHARGES
      AND RATIO OF EARNINGS TO FIXED CHARGES AND PREFERRED STOCK DIVIDENDS
                              (DOLLARS IN MILLIONS)


<TABLE>
<CAPTION>
                                            FISCAL YEAR ENDED  PERIOD ENDED           FISCAL YEAR ENDED JANUARY 31,
                                               NOVEMBER 30,    NOVEMBER 30,      --------------------------------------
                                                  1996            1995            1995            1994            1993
                                            -----------------  ------------      ------          ------          ------
<S>                                         <C>                <C>               <C>             <C>             <C>   
RATIO OF EARNINGS TO FIXED CHARGES

Earnings:
   Income before income taxes                    $1,572          $  883          $  594          $1,200          $  793
   Add: Fixed charges, net                        7,407           5,538           5,916           5,055           4,397
                                                 ------          ------          ------          ------          ------
      Income before income taxes and
        fixed charges, net                       $8,979          $6,421          $6,510          $6,255          $5,190
                                                 ======          ======          ======          ======          ======
Fixed charges:
   Total interest expense (1)                    $7,368          $5,512          $5,899          $5,020          $4,362
   Interest factor in rents (2)                      38              37              41              35              35
                                                 ------          ------          ------          ------          ------
      Total fixed charges                        $7,406          $5,549          $5,940          $5,055          $4,397
                                                 ======          ======          ======          ======          ======
Ratio of earnings to fixed charges                  1.2             1.2             1.1             1.2             1.2

RATIO OF EARNINGS TO FIXED CHARGES AND
   PREFERRED STOCK DIVIDENDS

Earnings:
   Income before income taxes                    $1,572          $  883          $  594          $1,200          $  793
   Add:  Fixed charges, net                       7,407           5,538           5,916           5,055           4,397
                                                 ------          ------          ------          ------          ------
      Income before income taxes and
        fixed charges, net                       $8,979          $6,421          $6,510          $6,255          $5,190
                                                 ======          ======          ======          ======          ======

Fixed charges:
   Total interest expense (1)                    $7,368          $5,512          $5,899          $5,020          $4,362
   Interest factor in rents (2)                      38              37              41              35              35
   Preferred stock dividends (3)                    101              80              97              85              82
                                                 ------          ------          ------          ------          ------
      Total fixed charges and preferred
        stock dividends                          $7,507          $5,629          $6,037          $5,140          $4,479
                                                 ======          ======          ======          ======          ======
Ratio of earnings to fixed charges and
   preferred stock dividends                        1.2             1.1             1.1             1.2             1.2
</TABLE>

(1)   Total interest expense for the period ended November 30, 1995 and the
      fiscal year ended January 31, 1995 includes capitalized interest.

(2)   Interest factor in rents represents one-third of rent expense, which is
      considered representative of the interest factor.

(3)   The preferred stock dividend amounts represent pre-tax earnings required
      to cover dividends on preferred stock.