In keeping with a modernization of corporate statutes in its home state, UMC Corporation decided in 2021 to discontinue accounting for reacquired shares as treasury stock. Instead, shares repurchased will be viewed as having been retired, reassuming the status of unissued shares. As part of the change, treasury shares held were reclassified as retired stock. At December 31, 2020, UMC's balance sheet reported the following shareholders' equity:

	($ in millions)
Common stock, $1 par	$	150
Paid-in capitalexcess of par		450
Retained earnings		960
Treasury stock (4 million shares at cost)		(20	)
Total shareholders equity	$	1,540

Required: a. Identify the type of accounting change this decision represents. b. Prepare the journal entry to effect the reclassification of treasury shares as retired shares.