This excerpt taken from the BP 6-K filed Apr 13, 2005.
Other post-retirement benefits: In May 2004, the FASB issued Staff Position No. 106-2 Accounting and Disclosure Requirements Related to the Medicare Prescription Drug, Improvement and Modernization Act of 2003 (the Medicare Act). The provisions of the Medicare Act provide for a federal subsidy for plans that provide prescription drug benefits and meet certain qualifications, and alternatively would allow prescription drug plan sponsors to co-ordinate with the Medicare benefit. The Company reflected the impact of the legislation by reducing its actuarially determined obligation for post-retirement benefits at December 31, 2004 and will reduce the net cost for post-retirement benefits in subsequent periods. The $577 million reduction in liability was reflected as an actuarial gain (assumption change).