When a company offers a defined benefit pension (i.e., one of those pensions whose benefits is based on years of service and ending salary), it has to pay an insurance premium each year to the Pension Benefit Guarantee Corporation (PBGC), a federal corporation formed under ERISA.  The PBGC steps in to continue pension payments in the event the company goes bankrupt and is relieved of its pension obligations.

The PBGC does not covered defined contribution pensions (i.e., 401(k), 403(b), etc) and it does not cover other benefits like retiree health insurance.  And lastly, there is a limit to how large a pension the PBGC will insure.  In 2009 PBGC had the following limits.

PBGC Maximum Monthly Guarantees for 2009*
Age 2009 Straight-Life Annuity 2009 Joint and 50% Survivor Annuity**
65 $4,500.00 $4,050.00
64 $4,185.00 $3,766.50
63 $3,870.00 $3,483.00
62 $3,555.00 $3,199.50
61 $3,240.00 $2,916.00
60 $2,925.00 $2,632.50
59 $2,745.00 $2,470.50
58 $2,565.00 $2,308.50
57 $2,385.00 $2,146.50
56 $2,205.00 $1,984.50
55 $2,025.00 $1,822.50
54 $1,935.00 $1,741.50
53 $1,845.00 $1,660.50
52 $1,755.00 $1,579.50
51 $1,665.00 $1,498.50
50 $1,575.00 $1,417.50
49 $1,485.00 $1,336.50
48 $1,395.00 $1,255.50
47 $1,305.00 $1,174.50
46 $1,215.00 $1,093.50
45 $1,125.00 $1,012.50
*  Amounts shown ignore IRC Section 415 limits, which may reduce payable amounts
** Assumes participant and spouse are same age

Source: Maximum monthly guarantee tables